摘要:

THE lecture delivered by Mr. J. L. Baird on Jan. 6 at the Physical and Optical Society's annual exhibition was very largely attended, and had to be repeated the same evening in order to prevent widespread disappointment. The attendance was a tribute to the intrinsic interest of the subject and to the expectations aroused by what little has become known of the lecturer's apparatus and achievements. Mr. Baird did not add to the general knowledge by what he said and did on that occasion. The situation appears to be that he has achieved a certain success in transmitting instantaneous images divided into some thirty vertical strips, each strip showing more or less correct gradation in a vertical direction. The picture composed by the strips is therefore very coarse-grained in one direction while sufficiently graded in a direction at right angles to it. The most important point about the transmission is that it uses diffusely reflected light, and not the light transmitted, say, by a lantern slide. To the latter transmission Mr. Baird will not consent to apply the term 'television ' at all, and in this we consider he is justified. The eye itself normally sees objects by diffusely reflected light, and television, to be worthy of the name and to accord with popular expectation, must do the sam6.Now this proviso is a very serious obstacle to overcome. For the 'candle-power' of a brightly illuminated face is approximately unity, whereas in kinematograph projection it amounts to thousands. True television, as defined by Mr. Baird, is therefore at least a thousand times more difficult than the transmission of shadows of moving objects such as has already been achieved by several inventors, among whom Ruhmer was the first in 1907. Mr. Baird appears to have succeeded in transmitting images of objects artificially illuminated to an extent equivalent to bright sunlight, and to have overcome the difficulties of synchronisation in transmitting and receiving within the same building. He also claims to have accomplished similar transmissions by radio over about ten miles, and to have transmitted living faces showing considerable detail. While giving him all credit for his very direct attack on a difficult problem, and for what he has demonstrably achieved, we must guard against an underestimate of the remaining difficulties. These will affect such things as synchronism, illumination, and detail.It is comparatively easy to keep two motors running at the same speed, even at a distance. But when a difference of phase of only one degree is capable of spoiling definition, the maintenance of the correct phase becomes a formidable task. Granted that Mr. Baird transmits the equivalent of 30,000 signals per second as against the 300,000 required for satisfactory television, it is easily seen that the problem of synchronism may become sufficiently acute to bar further progress. The figure of 300,000, on which most workers on this problem are agreed, is based upon the fact that a face alone, to be recognisable, requires some 3000 graded elements. Most press portraits comprise at least 10,000 such elements; and in order to produce the illusion of continuity or motion, there must be at least sixteen transmissions of the whole picture per second. From the information available-and it must be remembered that Mr. Baird has not disclosed the essential details of his method-it appears highly probable that little further progress need be expected along the lines chosen by him. The illumination seems to have been driven to its farthest limit, and the recent claims to have transmitted ' outlines ' by infra-red rays mark no advance towards television with diffusely reflected light. The subdivision of the image by a disc of spirally staggered lenses seems incapable of extension, and the suggestion thrown out in the course of the lecture, that several photo-electric cells (and several radio-frequencies) might be used simultaneously, only serves to emphasise difficulties already known to exist.It is to be regretted that, possibly on account of patent considerations, Mr. Baird has hitherto been unable to submit to a proper authentication of his claims by a learned society. For aught his recent audience could say, the invention might be a mere plaything, with no more resemblance to television than a toy engine has to the real thing. That is not the way to convince a sympathetic audience of experts who are expected to judge of the merits and prospects of an invention. There are at least three pioneers in the field who seem to be on the verge of a complete solution of the television problem. Belin in France, and Alexanderson and Jenkins in America, are all approaching the problem by way of the transmission of photographs, which they accomplish in great perfection. Dr. Alexanderson, chief engineer of the Radio Corporation of America, claims to be able to transmit a complete photograph in one second, and points out that if sixteen successive photographs could be transmitted in one second, the problem of television (or, at least, of telekinematography) would be solved. He adds, however, that the difficulties, especially of synchronism, increase as the square of the speed. It is well to remember that the earlier solutions proposed after the discovery of the light-sensitive property of selenium did not require the synchronisation of moving parts at the sending and receiving stations. But a multiplicity of wires, one for each picture element, is out of the question, and so is a multiplicity of radio-frequencies. Unless, therefore, some device such as Dr. Fournier d'Albe's acoustic resonator system can be employed for the simultaneous reception of a medley of signals, the question of synchronism, effective both in speed and phase, will arise; and when we realise that the synchronism required is that of two ' pencils ' which traverse the picture completely in a sixteenth of a second, and in doing so describe several hundred lines, the mechanical difficulties may well appal us. The speed with which the stimulus can be applied at the transmitting end is great enough nowadays, for the action of a photo-electric cell shovs no appreciable lag, and the use of a Braun cathode ray tube at the receiving end, first suggested, we believe, by Mr. Campbell Swinton, will solve the speed problem there.There remains the problem of sensitiveness to illumination at the receiving end. Mr. Baird does not tell us what he uses. His results suggest a potassium photo-electric cell for ultra-violet, and either selenium or bolometer for the infra-red. If he has discovered any reagent of greatly superior power, that discovery alone would entitle him to our gratitude, and would constitute a valid claim even though all his other devices had been anticipated by others. The policy of withholding publication of an essential item does not commend itself to modern inventors. It savours too much of medieval practice, and usually defeats its own object of securing to the inventor the fruits of his invention. It would be a source of satisfaction to us if one of our countrymen were the first to provide a practical solution of a problem of this magnitude, a solution such as the civilised world has been expecting for some years. If the solution has been reached without the scientific, engineering, and financial resources at the disposal of rival inventors, it will appeal very powerfully to our sympathy and imagination. But for the present, and on the evidence supplied, the scientific world will probably prefer to reserve its judgment.

ISSN:0028-0836    

DOI:10.1038/119073a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

QUITE a dozen years ago statements began to aQ5 appear in our public press announcing that " Darwinism was dead," and so often has this assertion been repeated in more recent days that there has arisen in the public mind a fear that some sort of fatality has overtaken the reputation of the great naturalist. If by Darwinism is implied the body of fact, inference, and doctrine contained between the covers of " The Origin of Species," then assuredly Darwinism is not dead, for the revolution which that book began to work in the minds of thoughtful men sixty-seven years ago still continues its forward and unchecked progress. The essence of Darwin's teaching is to be found in the last paragraph of the introduction he wrote for the first edition of " The Origin," and is repeated in all the later editions. There Darwin states that " I can entertain no doubt, after the most deliberate study and dispassionate judgment of which I am capable, that the view which most naturalists until recently entertained, and which I formerly entertained-namely, that each species has been independently created-is erroneous." Through Darwin's influence 'special creationists ' in all the leading nations of the world were transformed into 'evolutionists.' Thus in its widest sense Darwinism implies merely the acceptance of the belief that all living things' have been evolved from other and older living things. There is no book which seems so certain of a place in the permanent literature of the world as Darwin's " Origin of Species."That Mr. H. G. Wells, trained under Huxley, should be a Darwinist in this wider sense occasions no surprise; but it was scarcely to be expected that Mr. Belloc, a devout son of the Roman Catholic Church, should be of the number. Yet, like Darwin, Mr. Belloc rejects special creation and accepts evolution; he even reproves Mr. Wells for being ignorant of the fact that " the conception of the Old Testament as an exact text-book of history and science, not a word of which must be taken as allegory or generalisation, was mainly confined to England and to her colonies. The Catholic Church never. held it or could of its nature hold it " ("A Companion," p. 32). Mr. Belloc assures his readers that the theory of evolution is old, and that " the ancients and fathers of the Church " were familiar with it. Darwinism is confined by many people to cover merely the theory enunciated in the " Descent of Man." When used in this more limited sense Darwinism cannot be considered as dead, for I do not know of any living anthropologist or student of the human body who believes that man arose by a special act of creation. Anthropologists may differ as to the kind of ape from which humanity has been evolved, and as to the geological date at which its face was turned man-wards, but on the evidence now before them, which grows in volume and in trustworthiness every year, most of our authorities share Darwin's belief that the anthropoid apes and man have sprung from a common stem. In this narrower sense Mr. Wells is a Darwinist, but so adroitly does Mr. Belloc cover his verbal tracks with a smoke-screen that it is somewhat difficult for his readers to decide whether as regards man's origin he is a fundamentalist or a Darwinist. He quotes with approbation the belief held by " St. Thomas, the great teacher of the Middle Ages," to the effect that "the creation of man was not mediate but direct." St. Thomas must, on this evidence, be classed among the fundamentalists. Mr. Belloc, however, gives his verbal assent to this narrower form of Darwinism which the fundamentalists find so objectionable; he believes in evolution; he regards the process by which man reached his present estate as open to debate; he speaks of " the moment when a true man existed at all"; he directs Mr. Wells's attention to -the fact that certain tests show a close blood affinity between man and anthropoid. With such evidence before us we cannot say that Darwinism-even in this narrow sense-is dead.Yet in justice to Mr. Belloc it should be added here that he rejects two points in Darwin's theory of man's origin. Darwin believed that man's rise from apedom was a slow and gradual process, and he hoped that the evolutionary forces which had lifted him thus high might lift him still higher. Mr. Belloc, on the other hand, prefers to believe that man's emergence was of the nature of a leap, and that he is now and will ever remain a 'fixed type.' Our scanty knowledge of fossil ape and man, and our much fuller information regarding their embryological histories, are altogether against Mr. Belloc's beliefs and in favour of Darwin's postulates, which have been rightly adopted by Mr. Wells. There is a third and more restricted sense in which the term Darwinism is used. As an intrinsic part of the machinery which he regarded as being concerned in the evolution of living forms, Darwin introduced the principle or law of " Natural Selection," which he defined thus: " This preservation of favourable individual differences and variations, and the destruction of those which are injurious, I have called Natural Selection or the Survival of the Fittest " (" The Origin of Species," sixth edition, p. 63). There can be no doubt that Darwin claimed the recognition of this law and its application to the problems of evolution as his particular discovery. " Natural Selection," writes Mr. Belloc, " is the only thing that properly can be called Darwinism," and he reproves Mr. Wells for being unaware that Darwinism in this sense has been " riddled for a generation "; that it is " done for"; that it is "shaky"; that it is "nonsense"; that it, is " old and exploded "; that it is " moribund "; and also that it is " quite dead."Mr. Belloc devotes many pages to the exposition of Darwin's law of selection, and so little is the resemblance of the exposition to the original that one is forced to the conclusion that he has never read even the first chapter of " The Origin of Species." Darwinism as expounded by Mr. Belloc is certainly dead; indeed, it was never born. One does expect a historian, especially one who is ever accusing his antagonist-very unjustly-of being ignorant of recent events in the history of Darwinism, to be familiar with some of the chief happenings which followed the publication of " The Origin of Species." Mr. Belloc apparently does not know that Mr. St. George Mivart (" On the Genesis of Species," 1871), a convert to the Catholic Church, and one of the ablest anatomists of his time, formulated all the arguments which he now brings against Darwinism, and based them on an expert and first-hand knowledge of living things, such as Mr. Belloc can lay no claim to. Nor is he aware that Darwin, patient with even unscrupulous and prejudiced opponents, devoted twenty-eight pages of the sixth edition of " The Origin of Species " (1872) (pp. 176-204) to answering Mivart's criticisms. From first page to last of this sixth edition, Darwin protests against those early critics who supposed that the variations utilised by natural selection occurred' singly' and ' accidentally '; he admits time after time that although he does not know the ' efficient cause ' which brings variations into existence, yet he is certain that their appearance is regulated by many laws, "some few of which can be dimly seen," one of these being the law of ' correlated growth' whereby a whole series of structures may be modified together so as to serve more advantageously some functional purpose.Mr. Belloc resuscitates this ancient misrepresentation of 'accidental' and 'single ' variations and is thereby enabled, sitting in his armchair, unoppressed by any sense of modesty or burden of knowledge, to enumerate a dozen arguments, each ticked off after another with a triumphant emphasis, all of them demonstrating that the author of natural selection was an uncommonly stupid man and his modern critic a very clever fellow. One who presumes to criticise Darwin's " Origin of Species," especially from a mathematical point of view, should have known that Prof. Fleeming Jenkin (" The Origin of Species," sixth edition, 1872, p. 71), in 1867, had demonstrated the impossibility of a new breed or variety arising by natural selection if it had only ' accidental' variations to work upon, and that Darwin had shown this erudite professor wherein his error lay. Mr. Belloc knows nothing of this. Nor does he seem to be in touch with what is happening all around him now. It is difficult to believe that any one who sees the unceasing struggle which goes on everywhere and every year for the possession of the continents of the world and has been waged since the dawn of history, a struggle which is attended by the spread and domination of a few favoured races and the retrocession and obliteration of many less favoured races, can doubt the potency of Darwin's law of selection as a factor in the process of evolution. We may not like the way in which evolution works out its effects, but I do not think man, devise as he may, can escape from them. Certainly animals and plants in a state of Nature cannot. In ihe five and fifty years which have elapsed since the sixth and last edition of " The Origin of Species " was published, we have learned much concerning how evolutionary processes work in the world of living things, much that was unknown to Darwin. We know now something of the complex laws of heredity, and of the physiological means whereby the growth of the body is regulated, so that its several parts are modified together and made to serve a functional purpose. An example mentioned by Mr. Belloc (" The Companion," p. 22) will serve to illustrate the direction in which our knowledge has improved. After citing one of Darwin's early critics to prove that " chancemade variations " could never have provided functionally useful structures, he proceeds thus: "And another biologist has well said-What is the survival value of horns without the structure to support them and muscles to use them ? " Having set down this question, Mr. Belloc proceeds to answer it. " The mathematical chances," he informs his readers, " are millions and millions to one " against " the possibility of such a thing. Grant Design moulding all nature-that is, Godand this process is explicable." The impious biologist of to-day does not find it necessary to call in any divine or supernatural power to explain the multitude of changes which accompany the growth of horns in a young bull or antlers in a stag; the deity Mr. Belloc appeals to lies in the testes of these animals ! The biologist knows that if a certain substance or hormone formed in the testes is withheld, none of these changes take place; if they are permitted to enter the circulation, then as the horns grow the bones and muscles of the neck increase in size and strength, the lumina of blood-vessels expand, and, what is still more wonderful, the temperament of the animal is transformed. The discovery of hormones, if it renders a direct appeal to the Almighty no longer necessary, does not in any way invalidate or lessen the efficiency of Darwin's law of natural selection; the hormone theory simply helps us to explain how variations of an adaptative nature can and do arise.What is here written will suffice to show that Darwinism, in whatever sense we construe it, is neither an exploded creed nor a dead doctrine, and that those who assert the contrary not only min against the light of truth, but also commit a crime by poisoning the springs from which a trusting public drinks its information. It would be unfair to the memory of St. George 1Xivart were I to conclude without indicating, however briefly, the remarkable manner in which he anticipated in 1871 (" The Genesis of Species ") the arguments which Mr. Belloc has brought against Darwin in 1926. Mr. Mivart began by asserting that a belief in evolution " was perfectly consistent with the strictest and most orthodox Christian theology "; Mr. Belloc echoes this statement but substitutes 'Catholic' for 'Christian.' Mr. Mivart called the " Fathers and Ancients " as witnesses for the orthodoxy of the theory of evolution, singling out St. Thomas for special mention; so does Mr. Belloc. Mr. Mivart reproved Darwin for his total ignorance of the " philosophy and teaching of the Catholic Church "; Mr. Belloc scolds Mr. Wells for the same offence. Mr. Mivart believed that structural modifications of a really useful kind were wrought by a supernatural agency; so does Mr. Belloc. Mr. Mivart believed that by a miraculous intervention man became possessed of a soul only in the last stage of his evolutionary progress; this apparently is also Mr. Belloc's belief. Darwin, as I have already mentioned, took infinite pains to answer Mr. Mivart's scientific objections, and I thought every one knew that Huxley had answered his theological arguments. in a famous essay (" Mr. Darwin's Critics," 1871, Huxley's " Collected Essays," vol. 2, p. 120), but it must have escaped Mr. Belloc's attention, for he never alludes to it. Yet it is an essay which he might read with advantage, as should every one who honestly tries to reconcile Catholic beliefs with the truth of science. Even Mr. Mivart, in the end, found a reconciliation impossible. His later books were placed on the Index Librorum Prohibitorum, and in January 1900, when his last illness was upon him, he was excommunicated by Cardinal Vaughan because he dared to assert what his investigations into science had taught him. Such was Mr. Mivart's fate, and one wonders what would have happened to the author of " The Origin of Species " if his life had fallen in Catholic places and had his beliefs been in the keeping of Rome.

ISSN:0028-0836    

DOI:10.1038/119075a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

C LASSICAL electrodynamic theory has had considerable success in explaining many of the phenomena of atomic physics, but there are other facts which seem to necessitate a radical departure from this theory. During the first quarter of the century many attempts were made to meet these difficulties by means of special assumptions and rules, which constituted the quantum theory. Although these methods have had remarkable success in the interpretation of a restricted region, it has long been felt that such a procedure, designedly adopted with a particular end in view, was not satisfactory and that a more general theory was required. In 1925 Heisenberg put forward a new theory of quantum mechanics which seems likely to have far-reaching consequences, even if it does not lead to a complete solution of the problem. One of the fundamental ideas employed by Heisenberg is that only such things as are directly open to observation should enter into the mathematical formulation. He considered it advantageous to avoid every notion which cannot be connected with experiment, and so eliminated all ideas of motion within the atom. We are unable to assign to an electron a special position in space at a special instant of time, so that, so far as our observations are concerned, an electron orbit does not exist. In the mathematical statement of the new theory, developed in association with Born and Jordan, the continuous variables of the classical theory are replaced by systems of discrete quantities (matrices) which can be expressed by means of algebraic equations.Although the theory of matrices is founded on the work of Cayley, Sylvester, and H. J. Smith, and is about seventy years old, some mathematicians and most physicists are unfamiliar with the ideas involved. As pointed out recently in these columns (NATURE, August 28, 1926, vol. 118, p. 295), the fundamental notion is by no means difficult to grasp. Cayley considered a square arrangement of numbers as constituting a matrix, realising the value of treating it as a single magnitude. Thus nine numbers put in square formation, three by three, are called a matrix of order three. For example: 1, 2, 34F 5, 6 7, 8, 9We may also deal with a rectangular matrix of mn numbers, arranged in m rows and n columns. The matrix is to be thought of as a compound unit, an assemblage of numbers arranged in order but constituting a single entity. A simple geometrical illustration is afforded by taking [x, y] as specifying the position of a point in a plane. Unless x =y, the point [x, y]is not the same as the point [y, x]. Such an entity, which mav include a row of n numbers, is a special case of a matrix of rank one. The determinant of a matrix must be distinguished from the matrix itself, just as the area of a triangle must be distinguished from the triangle itself. Cayley gave rules for adding, subtracting, and multiplying matrices, and it is of importance in the present connexion that the product AB of two matrices A and B is not generally equal to the product BA.The most interesting part of the volume under notice is undoubtedly that in which Prof. Max Born has described in some fifty pages the development of the new quantum mechanics. In the classical theory a particular co-ordinate may be represented by a Fourier series comprising the various components, but in the new theory the collection of all possible vibrations is to be regarded as a whole in a quadratic scheme forming an infinite matrix. If q denote such a co-ordinate matrix and p an impulse matrix, instead of assuming that the product qp is equal to the product pq, we must introduce a new postulate, namely, pq qp=/(2i),where h is Planck's constant and i is the square root of -1. P. A. M. Dirac of Cambridge has expressed the new theory in a different form by means of a specially devised quantum algebra in which the quantum variables satisfy all the ordinary laws of algebra, excluding the commutative law of multiplication. Instead a special quantum condition is postulated, involving Planck's constant and equivalent to that stated above. Schrodinger starts from the idea suggested by de Broglie that an atomic system is not to be represented by a trajectory, that is, by a point moving through the co-ordinate space, but must be represented by a wave in this space. From this startingpoint he develops a wave-theory of matter, and obtains from a variation principle a differential equation which the wave function must satisfy. This equation turns out to be closely connected with the Hamiltonian dynamical equation which specifies the system. When the general solution of this equation is known, matrices to represent the canonical variables may easily be obtained satisfying all the conditions that they have to satisfy according to Heisenberg's matrix mechanics. The mathematical equivalence of the theories is thus established, and it is shown that (in the words of Schrodinger) " the wave-mechanics and the matrix mechanics are mathematically identical." The concept of characteristic oscillations in the atom and Schrodinger's theory based upon it represent a most significant contribution to the development of the quantum theory. " From the formal mathematical point of view it includes the whole of the Heisenberg-Born-Dirac matrix theory, and gives, moreover, a simplified, practically convenient method of finding the matrices. Beyond this, it opens new avenues of thought and seems to afford our first glimpse of the true nature of the I quanta " (Epstein).The development of the new theory is taking place with great rapidity, and several applications have already proved successful; only a few of these can be mentioned here: Pauli has shown that the Balmer formula for the hydrogen spectrum can be accounted for quantitatively, as well as the influence of electric and magnetic fields on this spectrum. A theory of the Stark effect based on Schrodinger's ideas has been presented by Epstein, who considers the radiation from a hydrogen-like atom in an electric field. The calculated positions of the components of the spectral lines practically coincide with those obtained in Epstein's old theory, which gave excellent agreement with experiment. The main interest lies in the expressions for the intensities, which agree with the observed values better than those deduced by Kramers from the correspondence principle. Schrodinger himself has discussed the same problem. Brillouin has treated the subject of rotation spectra by the calculus of matrices and has found experimental verification for certain of the theoretical deductions. Dirac has discussed the extension of the theory to relativity mechanics, and in particular to the theory of Compton scattering, and obtained results which can be tested by experiment. One test of a scientific theory is its comprehensiveness, and the wide sweep of the new quantum mechanics is shown not only in the various ways of formulating it in mathematical language, but also in the physical ideas that may be associated with it. It is probable that the views of the quantum suggested by E. T. Whittaker and by the present writer, in which its magnetic aspects are emphasised, may be simply related to the new theory. In a recent paper Whittaker has described a simple light quantum in which a disembodied magnetic molecule, travelling with the speed of light, forms a singularity on the wave front and confers upon it the desired quantum properties. It may be suggested that such a quantum is related to a quantum magnetic tube on one hand, and to Schrodinger's wave mechanies on the other. In discussing the relation between the quantum theory and the classical laws, Dirac remarks that the new theory " suggests that it isnot the equations of classical mechanics that are in any way at fault, but that the mathematical operations by which physical results are deduced from them require modification. All the information supplied by the classical theory can thus be made use of in the new theory."

ISSN:0028-0836    

DOI:10.1038/119077a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

THE working up of the by-product, glycerol, of the soap and stearin candle industry is of such economic importance that the author has felt justified in allotting this entire volume to the subject of glycerol. In attempting to prepare a complete treatise (as the present volume claims to be) on any branch of chemical industry, great difficulties confront the writer. Many books of such a type, while apparently satisfactory to the technological student, are often to the works' chemist of less value and perhaps incomplete. This is mainly due to the unwillingness of manufacturers (very often for good reasons) to divulge details of processes which may be of indirect help to rival firms. In the work under review it may justly be claimed that the author has collected together a great many practical details of modern glycerol plants and processes, especially in the sections dealing with the working of evaporators and stills. In fact, in no similar single publication, at least in English, can such a mine of useful information be obtained. The author has been extremely fortunate in having secured the valuable aid of various industrial firms, including still-makers, in the compilation of his data. In addition, as in the previous two volumes of this series, references are given to practically all the important related patents, including even those at present of no industrial significance, on the subject of glycerol production and application. A useful section on polymerised glycerol and glycerol substitutes is also included. In the final section the commercial valuation and analysis of glycerol and the various specifications for products of different grades are treated in a very satisfactory manner.An exhaustive index for the three volumes is also included in the present work, with cross references. The complete work forms an indispensable reference treatise on the technical literature of the soap and delegent industry.

ISSN:0028-0836    

DOI:10.1038/119079b0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

THIS handbook is for the use of medical practitioners; it contains a foreword by Sir John Robertson, the Medical Officer of Health for Birmingham, who is keenly alive to the part which this form of therapy is playing and is likely to play in the near future. Doctors have now to know something of the technique of the sources of ultra-violet radiation, of the effects to which the rays give rise, and of the diseases which are favourably influenced thereby. The book under notice, in a restricted sense, provides this information; the authors write practically only upon their own experiences, and these appear to be restricted to thd use of the mercury vapour lamp. They give an excellent account of these lamps, of the way in which they should be used, and of the diseases for which their use is warranted. We can understand, however, that many medical practitioners will want to know something about the open arcs which are largely used in many of the big light clinics.Dosage in this form of therapy is still rather primitive; the 'normal dose ' according to the authors may be taken to be "that which will produce in the patients' most sensitive skin surface the faintest perceptible erythema." No doubt in time there will be established a physical unit of ultra-violet radiation which will be of service in medicine, and it is to be hoped that the interval will not be so prolonged as has been the case in X-ray therapy.

ISSN:0028-0836    

DOI:10.1038/119080a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

AT the present moment there is a widespread misunderstanding of the nature of the evidence that is now available to suggest how, when, and where the practice of tilling the soil began. It is not my intention to traverse the whole field so fully explored in 1921 by Prof. Thomas Cherry in his address on “The Discovery of Agriculture,” delivered at a meeting of the Australian Association for the Advancement of Science; but new information is now available that confirms the accuracy of his statement, which should dispel the doubts and difficulties that have arisen.I suppose most people would be prepared to admit that the invention of agriculture was the beginning of civilisation. It involved a really settled society and the assurance of a food supply. Hence it created the two conditions without which there could have been no real development of arts and crafts and the customs of an organised form of society. But for many years there has been a sharp conflict of opinion as to how and where this momentous event took place. In 1901 it was my good fortune to become associated with Profs. George A. Reisner and Albert M. Lythgoe in the most thorough study of an early pre-dynastic site (Naga-ed-Der in Upper Egypt) that has ever been made. In the course of examining the well-preserved bodies found in this cemetery, I recovered from the alimentary canals of a large number of bodies the food which these people had consumed about sixty centuries ago. This material I sent for examination to Dr. Fritz Netolitzky, the professor of pharmacology in the University of Czernowitz, who is the leading authority on the subject. Prof. Netolitzky published an account of the results in the Zeitschrift fur Untersuchung der Nahrungsund Genussmittel (1911, Bd. 21, p. 607) and Die Umschau (1911, pp. 45 and 95). At the same time he sent me a letter summarising his results, which I quoted in the little book, " The Ancient Egyptians," I was then engaged in writing.The statement that barley was the staple article of diet in Egypt from the earliest pre-dynastic period has passed without any notice whatever during the last fifteen years, excepting the use made of it by Prof. Thomas Cherry. In recent discussions that have been taking place at the meetings of the British Association, the Royal Anthropological Institute and elsewhere, as to the beginning of' agriculture in Egypt, I am told that no reference of any sort has been made to these fundamental facts, the neglect of which must necessarily sterilise any real investigation of this most important issue. Dr. M. Gompertz has directed my attention to a fact (which I had not realised until then) that in his memoirs published in 1911, Prof. Netolitzky has not made any unequivocal statement on the barley question. In fact, the only place in which the issue is explicitly mentioned is his memoir in Die Umschau (1911), which is almost identical with the private letter its author sent to me in the same year. But there is an important difference between the letter and the published statement. In the latter the statement is made that in almost every sample of the early pre-dynastic Egyptians' food, which I sent to Dr. Netolitzky, there is evidence of the husks of " the barley-wheat-type " (Gersten-Weizentypus), whereas in Dr. Netolitzky's private letter the corresponding sentence ran " in almost every sample there was evidence of the husks of barley." The difference between these two statements was so vital that I wrote to Prof. Netolitzky and asked him for further information. In a letter dated Nov. 25, 1926, he says:" Barley is the chief cereal found in the Naga-edDer specimens. I am of the opinion that wheat was not eaten at that time, for we certainly should have found it if it was present in the specimens, because we can detect the much softer fragments of the husks of barley where the much harder and more characteristic husks of wheat are completely lacking. We can therefore assume that the Naga-ed-Der people did not use wheat; at any rate it is absent in the numerous specimens that you sent me. Some years ago the late Dr. Bruijning, of the Agricultural Experimental Station at Wageningen, wrote to me to say that he had come to the conclusion that wheat first came into Egypt at the beginning of the dynastic period. Schulz ('Die Geschichte der kultivierten Pflanzen,' 1, 1913) expresses the conclusion that barley was the first cereal used in the Nile Valley. " Prof. Netolitzky has also been kind enough to send me a paper by Frau Hedwig Gherasim (" Neue Kennzeichen der Getreidespeizen und Beitriige zur Bestimmung prdhistorischer Pflanzenfunde," Pharmaz. Monatsheften, 1921) which contains the following statements. She says that while Prof. Netolitzky was convinced barley was the chief cereal used by the pre-dynastic Egyptians, at the time she began her research he had not definitely excluded the possibility-his letter to me in 1911 shows it to have been only a possibility-that wheat might also have been used, because in the material from Naga-ed-Der there was a number of husks of indefinite type (his barley-wheat-type). The solution of this problem he postponed for further investigation and then entrusted the task to Frau Gherasim, who says that she has now examined Prof. Netolitzky's material and has been unable to find a single case in which the diagnosis of wheat can be established, whereas there is ample evidence that barley was present in most of the specimens she examined. She says this discovery is of extraordinary interest and importance, for it definitely establishes the fact that the pre-dynastic people did not eat wheat. The number of specimens is so great that such an assertion can be made with complete confidence. The earliest example of Triticum dicoccum appears to be that found by Borchardt in the foundation at the west end of the offeringgranary in the temple of King Sahure of the fifth dynasty. Dr. Cherry and others have pointed out, however, that it may have been in use in earlier dynastic times.The question of the cultivation of barley in Egypt is not merely a matter of local interest, but also involves the much wider problem of the origin of civilisation itself. During recent years there have been repeated discussions as to the relative antiquity of Sumerian and Egyptian civilisation. Prof. Breasted now tells us that this question has been definitely settled once for all. In his book, " The Conquest of Civilisation," which was published a few weeks ago, he makes this statement (p. ix): " Perhaps the most far-reaching consequences among newly-discovered sources are the new cuneiform tablets with [Sumerian] dynastic lists at last determining the maximum age of the earliest Babylonian written documents. They are at most a little earlier than 3000 B.C. Thus it is now a finally established fact that civilisation first arose in Egypt, followed a few centuries later by Babylonia." The opinion he expresses agrees with that of most of the experts of Great Britain, Europe and America who have first-hand knowledge of the material found within recent years in Mesopotamia.It is now generally admitted that the first dynasty of Ur can be dated at 2900 B.C., and that the most remote age that can be assigned to it is 3100 B.C. Painted pottery has been found in Susa [Elam] which may be, and probably is, earlier than the first dynasty of Ur; but this has been equated with the pottery distinguished as Susa II. This follows Susa I., which it is generally estimated corresponds to the middle pre-dynastic period in Egypt. In other words, in Egypt the whole duration of the early pre-dynastic period is definitely anterior to any evidences of civilisation that have been found in Asia or in fact anywhere in the world. If, then, the early predynastic evidence reveals the presence of cereals and suggests that agriculture was then being practised, we have positive evidence of the most significant kind that civilisation began in Egypt. We know also that people in Egypt at this time, many centuries before the metal copper was known, were using the copper ore malachite, which there is every reason for believing was obtained from the Wady Alaq Nubia. These and scores of other facts to which I have been constantly directing attention, in season and out of season, during the last fifteen years, establish on a firm foundation the certainty that civilisation, not merely agriculture and the working of metals, but also the invention of all the essential arts and crafts, customs and beliefs that go to the making of early civilisation, were first invented in the Nile Valley. The fact that the alimentary canals of all those earliest Egyptians contained barley is surely certain evidence that barley was growing in Egypt at that time. Whether it was indigenous or not we have of course no direct evidence to prove, because every foot of land that can be cultivated in the Nile Valley has been turned over countless millions of times during the last sixty centuries by an unbroken series of fellahitn. But the fact that wild barley is found in the north-east corner of Africa, both on the Mediterranean littoral and in the regions to the south and east of Egypt, suggests that it was also growing in the Nile Valley when men first made their way into that strip of land.The only alternative is to assume that the earliest Egyptians brought barley into the country with them. I need scarcely say that this is a mere speculation, in support of which there is no evidence of any sort, not even a suggestion of its likelihood. The conclusion that is forced upon us is that the earliest settlers in the Nile Valley found barley growing there in a wild state and made use of this natural food supply. Living under such ideal conditions, the population, in course of time, increased to such an extent that the natural supply was inadequate to support them. Then it can be assumed men imitated the natural processes which they had watched year by year for unknown centuries, and by extending the area of irrigation instantly devised the art of irrigation and the invention of agriculture. This is the only reasonable interpretation of a vast mass of evidence.

ISSN:0028-0836    

DOI:10.1038/119081a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

THE letters which have recently appeared in NATURE on the relationships of wireless reception and terrestrial magnetism suggest that a few remarks from the point of view of a magnetician may not be superfluous. First, on an historical point, it should be remembered that estimates of the altitude of a stratum of high electrical conductivity were made long before the times of wireless communication. Cavendish (Scientific Papers, vol. 2, p. 233) in 1790 obtained on strictly scientific grounds an estimate of from 84 to 114 km. for the altitude of an auroral arc. Prof. Störmer's methods of high precision have supplied numerous results for the lower level of aurora, which have long been well known. The levels he has found show variations with similar limits to those recently obtained by Appleton and Barnett (Roy. Soc. Proc., A, vol. 113, p. 450). Auroral observations, of course, are not possible by day, and we may hope to learn much from wireless which it might be difficult or impossible to derive from auroral observations.Again, the continual existence of high electrical conductivity in the upper atmosphere was first advanced as an hypothesis neither by Heaviside nor by Kennelly, but by Balfour Stewart. His statement will be found in 121 and 134 of his article on " Terrestrial Magnetism " in the ninth edition (epoch circa 1882) of the " Encyclop-Tdia Britannica." Stormer has shown that on special occasions aurora may extend to heights exceeding 600 km. Thus the term ' layer' applied to the space of high conductivity may not be a very appropriate one. But if any name is to be associated with a 'conducting layer' in the upper atmosphere, it should surely be neither Heaviside's nor Kennelly's, but Balfour Stewart's. The arguments for the existence of the ' conducting layer' on the side of terrestrial magnetism, even leaving aurora out of account, are by no means wholly theoretical. The strongest argument, in the opinion of the writer, is derived from the observed large universal increase of the diurnal variation of the magnetic elements as we pass from sunspot minimum to sunspot maximum. No such universal relationship has been observed in any meteorological or other element at the earth's surface, or in the lower atmosphere, except in the case of electrical earth currents, and these are generally believed, through their association with aurora, to be a direct consequence of the electrical currents overhead.It is this argument that has led practically all, if not all magneticians, to accept the upper atmosphere as the seat of electrical currents to which the regular diurnal variation of the magnetic elements is due. It is important to notice that it is the regular diurnal variation that has been observed to hold a parallel course to sunspot frequency. Speaking generally, years of few sunspots are less disturbed magnetically than years of many spots, but a year of many spots may not be a highly disturbed year. Thus 1893, though a year of sunspot maximum, was much quieter than either 1892 or 1894. All the magnetic elements show largely increased diurnal ranges in years of many sunspots. In Britain the increase seems larger for H (horizontal force) than for D (declination). In H an increase of 100 in Wolf's sunspot frequency has corresponded to a rise of about 100 per cent. in the range of the mean diurnal inequality for the year. The effect varies with the season of the year, the percentage rise in the range at Kew being roughly twice as great at midwinter as at midsummer. With increasing sunspot frequency, the tendency seems to be for the increase of amplitude to be larger in the 24-hour Fourier wave than in the waves of shorter period. This implies in the average day a reduction in the difference between day and night.There is an important difference in Europe between quiet and disturbed days. On quiet days the magnetic changes are much larger in the day than in the night hours; but during large disturbance the night hours are the most active. Large disturbance in Europe is much more common between 4 P.M. and 4 A.M. than between 4 A.M. and 4 P.m.; it is rare near 10 A.M. This difference between night and day is not, however, universal all over the earth. In the Antarctic, from 1911 to 1913, disturbance was much more in evidence during the day than the night hours. The distribution of magnetic disturbance throughout the 24 hours in high northern latitudes still apparently awaits investigation. Another result of interest is that the regular diurnal variation, whether in years of many or of few sunspots, tends to be larger on disturbed than on quiet days. This seems to imply that in addition to local irregularities in the conductivity of the ' conducting layer,' due presumably to the irregular distribution of the sources of ionisation, there is during magnetic disturbance a decided increase in the average conductivity. This phenomenon is comparatively trifling in southern England, but increases in prominence as we go north. If we may judge from what happened in the Antarctic in 1911 to 1913, it is exceedingly prominent in high magnetic latitudes, at least in years of few sunspots. At Cape Denison, the base station of the Australasian Antarctic Expedition, the range of the regular diurnal variation of H in the midwinter months for an average international magnetic character of 105-which implies only very moderate disturbance-was nearly six times the range from the international quiet days. Magnetic disturbance in these high latitudes is much larger and more persistent than in central Europe. This suggests that the natural place to study the relationships between wireless and magnetic phenomena is not the south of England but the north of Scotland, or still more northern regions. There are now magnetic observatories at Lerwick, Sodankyld (Finland), Matochkin Shar (Novaya Zemblya), Godhavn (Western Greenland), Meanook (Canada), and Sitka (Alaska). Wireless observations at two or more of these stations ought to provide in a short time a lot of interesting material

ISSN:0028-0836    

DOI:10.1038/119082a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

IN a recent issue of NATURE (Dec. 4, 1926, p. 805) there appeared a letter of Messrs. R. de L. Kronig and I. I. Rabi, in which they gave, on the basis of the new wave mechanics of Schrödinger, an expression for the energy of a symmetrical rotator,i.e.a rigid polyatomic molecule having two equal moments of inertia.A like result has also been obtained by F. Reiche (Zeit.f. Phys., 39, 444, 1926) using the wave mechanics. Furthermore, under the assumption that the molecule possesses a permanent electric moment along the direction of its figure axis, Reiche derived to first order approximation the addition to the energy expression caused by placing the molecule in an external electric field. Independently of Reiche, also using the wave mechanics, we have carried the calculation to the second order of approximation and have thus been able to compute the dielectric constant. We find for the total energy W*j, m, . of the molecule in the presence of an electric field of strength F TV*.mif=, n, m + h2/8r2 4A(tm, n t+1, ift.where Wj, is the energy of the molecule without electric field, as already given by D. M. Dennison (Phys. Rev., 28, 318, 1926) using the matrix mechanics. Ax represents the permanent dipole-moment, A the moment of inertia about an axis perpendicular to the figure axis, and j, m, and n three quantum numbers. The first of these may take all positive integral values not including zero, while the others may take both positive and negative integral values including zero, subject to the restriction that the absolute value of each shall not exceed the value of j. The function 4,m, , is a numerical factor depending only upon the quantum numbers: (ja -m2)( -n2) bob#=(2j l)(2j)3(2j + I)'sm, is the same expression, where only j + 1 is substituted in place of j. From the energy expression given above, the dielectric constant of a perfect gas is found to have the following value at high temperatures:47w N,a2 1+ 3KT' where T is the absolute temperature, N the number of molecules per unit volume, and k the Boltzmann constant. This result is in complete agreement with the value of the dielectric constant of such molecules already found by Kronig (Proc. U.S. Nat. Acad. Sci., I 2, 608, 1926) using the matrix mechanics, and it means that at high temperatures the dielectric constant obeys the law of Langevin-Debye. We have found that at usual temperatures the departure from this law cannot exceed a few per cent.It may be remarked that the second term in the energy expression given above predicts the existence of a Stark effect of the first order in the band spectra of symmetrical molecules, whereas for diatomic molecules an effect only of the second order is to be expected. The separation of the lines in the Stark effect of the first order for symmetrical molecules depends upon the magnitude of the dipole-moment and the field strength, but not upon the moments of inertia of the molecule. The intensity of the lines, on the other hand, is dependent upon the moments of inertia. The separation of the lines in the Stark effect of the band spectra of polyatomic molecules, which a simple calculation shows to be of a sufficient magnitude to be measured experimentally, thus provides a means of finding the dipole strength of such molecules. One finds AX/X -_ 22 x 10-6 with F=50,000 volts/cm. and A= 1 x 10-18 C.G.S. units. A detailed paper covering the work outlined here will appear shortly by one of us in the Physikalische Zeitschrift

ISSN:0028-0836    

DOI:10.1038/119083a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

THE excellent editorial in NATURE of Nov. 13 suggests a few comments. Several years ago, Lady Gregory came to the University of Colorado and lectured on the Irish drama. She insisted on the importance of each country or region fostering its own dramatic art, and cultivating dramatic expression among its citizens. Under such conditions, she urged, not only is there a quickening of the general intelligence, but also genius finds its appropriate setting and chance for appreciation. Surely the same argument may be used with reference to science. It is not possible to determine the native ability of various nations from such statistics as are cited by Dr. Slosson. Very much depends on popular recognition, and even the discovery of new chemical elements is largely controlled by opportunity. Although the genius is an asset of incalculable value, he is only of value to communities intelligent enough to profit by his labours. In 1914, 105,681 infants under one year died in Great Britain. In 1924 the number was only 65,259. In the same period the deaths per thousand were cut down from 23.9 to 19.3. This was not done through the brilliant inspiration of some genius, but by the incessant labours of thousands of relatively or absolutely obscure persons using the knowledge communicated by scientific men of all grades of distinction.My own interest in natural history was greatly stimulated by J. W. Taylor and W. D. Roebuck, who were preparing a " Monograph of the Land and Freshwater Molluscs of the British Isles." Their methods were in direct contrast to those of some monographers. We not rarely hear that so-and-so is monographing the . All specimens must be sent to him. No one else should have anything to say on the subject. By the time the great work appears, interest in its topic has so long been dead, that it is received with due reverence but little real joy. There are, of course, some fields of scienee which are necessarily cultivated in this manner. Only a few men of unusual training and powers, provided with unusual and costly apparatus, can do anything with them. The 'man in the street' is absolutely out of it, except as a possible contributor of funds. But in other fields this is not the case. Taylor and Roebuck, from the beginning, did everything to interest young conchologists in the possibilities of doing things, of making discoveries. The result was a great deal of enthusiasm and the accumulation of an enormous mass of data which eventually went into the monograph. It is lamentable to have to record that this beautifully illustrated and minutely detailed work has ceased publication, because the cost of printing is too high. As a contribution to national culture it would abundantly pay the country to continue the printing at the public expense. The moral seems to be, that whether we desire material benefits or increased happiness, bread or song, it is of the utmost importance to cultivate scientific interest among the people at large. This interest should not simply take the fornm of openmouthed astonishment at the works of the learned, but should be inspired by the hope and expectation of personal accomplishment, and the sense of having part in a great undertaking.

ISSN:0028-0836    

DOI:10.1038/119084a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

WHILE engaged in some experiments on mercury resonance radiation at Johns Hopkins University last spring, I became convinced that a less erratic and, if possible, more intense source than the usual watercooled quartz arc was almost a necessity for some kinds of work. A high-voltage discharge seemed likely to be much steadier than a low-voltage arc, and an obvious way of cutting down self-reversal due to normal mercury vapour was to use a gas for the discharge, with mercury present at a relatively low pressure, secondary processes keeping the mercury atoms largely in excited states. Experimental work was interrupted, however, and it was only recently that an opportunity arose for testing such a source in comparison with a regular quartz mercury arc.A quartz tube 7 mm. in diameter and 20 cm. long, provided with tungsten electrodes and containing argon at a pressure of about 6 mm. and mercury vapour at a pressure corresponding to 500 C. was excited by a small wireless transformer. The voltage across the tube was 1500. Used as a source, this tube produced an intensity of resonance of X2536 about half as great as that produced by a water-cooled quartz arc of the usual type. The arc was used without a magnetic field, but was cooled during the exposures at such a rate that it was extinguished in about a minute, thus producing the maximum intensity of resonance. The argon tube required no cooling or magnetic field and seemed perfectly steady and capable of indefinite operation without attention. I am grateful to Messrs. Foote and Mohler for apparatus used in these tests. It is probable that the intensity of the 'gasdischarge' source can be greatly increased. The pressures given above are approximately optimum values for the particular tube and excitation used, but the possibilities of obtaining greater intensity by using greater power input (the tube was comparatively cool), end-on illumination, other gases, perhaps an arc instead of a high-voltage discharge, etc., have not been tested. The device recommends itself as it stands, however, by its great convenience of operation and the ease with which it can be constructed in the laboratory. It appears likely that this source would be advantageous for resonance measurements when using a photo-electric cell instead of photographic plates.It is quite possible that such a gas-discharge tube has been used elsewhere as a source for mercury resonance. Dorgelo has used a similar discharge, although for a different purpose. The tube is also quite similar to those used by Wood and others for sodium, but its advantages over the much-used water-cooled mercury arc have seemed worthy of this notice.

ISSN:0028-0836    

DOI:10.1038/119085a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature