摘要:

THE seventh Comzffissior the work Britain up to Se are given of a undertaken with jort of the Forestry 'recently issued summarises been adboYiplished in Great "" ""a. J Interesting data "the 4vdodlands of Britain lendable persistence by the Commissioners. This census has shown that the existing woods amount to 2,958,630 acres, less than half of which can be considered productive. The latter fact appears to have come as a surprise to the Commissioners. The few experts having a knowledge of the forestry conditions of Great Britain could have foretold the result with considerable certainty, and probably not a few of the proprietors also, in the absence of any expert knowledge to guide them. It was common knowledge that considerable areas were maintained as game coverts, questions of their value for timber production being entirely subordinated to the premier object. The late Sir William Schlich often directed attention to this fact during the forty years he advocated an afforestation campaign in Britain. The heavy fellings made in the utilisable coniferous areas during the War have admittedly intensified the need for an afforestation programme, but have scarcely changed it. The question still remains one upon which the-Government and public, but chiefly the latter, must definitely make up their minds. The problem is a pressing one, but the costs of afforestating the several million acres which the experts are unanimous in admitting can be made more productive under trees will be very much higher than would have been the case had the work been done before the War. The present sanctioned programme comes to an end in 1929, and the Commissioners, in the report under review, express anxiety as to the continuance of the work and advise that it should be carried out on an enhanced scale. The report, in fact, is far more than a mere enumeration of the work of the year. It is more concerned with placing before its readers the work achieved to date and the lines upon which, in the view of the Commissioners, the next ten - year programme should be drawn.The arguments for and against the enhancement of the afforestation programme are weighty; for the true interests of the country, economic and otherwise, support the plea of the Commissioners for an enhanced programme. Those against are chiefly concerned with the great expense involved, and the added factor that an experienced forest service has yet to be built up. After the wars of a century ago, prices remained high for a considerable period and gradually dropped. It may be hoped that the future, how distant none would dare to say, will see a similar reduction. This would mean that plantations now being made at £5: 16s. to £7:10s. an acre might cost only half the amount. The cost of buildings, etc., for small-holdings would likewise be reduced; and so forth throughout all the various branches of forest work. Up to Sept. 30, 1926,186 small-holdings (the average cost of 63 new buildings during 1926 was £623 apiece) had been completed. It is hoped that 750 small-holdings will be completed or in process of establishment (the limit in sanctioned cost is £800 apiece) by the end of 1929. It is stated that their number could be increased to 3000 or 4000 in the next ten-year period. The Commissioners admit that they have only had two and a half years' experience of this form of rural settlement. Experts in Great Britain disagree as to whether such a form of settlement is practicable. It is a common method in France; but small-holders there work 10 hours a day as a minimum during the spring and summer and are far thriftier than our people. The cost of ' planting ' is shown in a curious way in the Report. All expenses during the first year of formation, including weeding, arc termed the cost of ' planting.' If 50 per cent, of the plants fail and have to be replaced, this operation is shown under ' establishment' of the plantation. Presumably if the whole of the trees under ' planting ' failed, the replanting of the plantation would be shown under ' establishment,' a somewhat complex puzzle to set the forest officer in charge, say, fifty years hence. The Report shows (Table E. 5) that during the seven years £132,767 were spent on planting and £35,061 on ' beating up,' i.e. replacing failures in the plantations. This amounts to something more than 25 per,cent, failures in the first plantings. For 1926 the figures are £28,621 and £13,071, slightly less than 50 per cent, failures. No private proprietor could afford to plant if ' beating up ' oil this scale had to be faced. It is scarcely a justification for speeding up the planting campaign during the next ten years, which is so warmly advocated in the Report.That much good work has been accomplished by the hard-working officers of the young service under the Forestry Commissioners is undeniable. That experience can only come with increased knowledge and practice is equally und

ISSN:0028-0836    

DOI:10.1038/120177a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

THE artificial disruption of many of the chemical elements can be regarded as a direct outcome of the study by Geiger and Marsden of the scattering of a-particles by matter, and the formulation, in 1911, of the nuclear theory of the atom by Sir Ernest Rutherford. Theoretical work of Darwin on collisions of re-particles with the nuclei of atoms was supplemented by the experimental work of Marsden and Lantsbcrry, who discovered the production of H-rays in hydrogen when a-particles collide with the nuclei of hydrogen atoms. The later development of this work by Sir Ernest Rutherford revealed the production of H-rays when nitrogen is bombarded by a-particles, and in this we have the first instance of the artificial disintegration of an element by a-rays. Since 1919, the subject has been actively pursued by Rutherford and Chadwick in the Cavendish Laboratory at Cambridge, and the ejection of H-particles from the nuclei of many of the lighter elements has been established, the effects being most marked for elements of odd atomic number. Unfortunately, experiments of this nature require the use of appreciable quantities of radium, and this undoubtedly accounts for the fact that so fascinating a study has not been taken up in many more laboratories. In 1922, however, the authors of the present monograph commenced work oil similar lines at the Vienna Radium Institute, which, since it was opened in 1910, has been an active centre of radioactive research, and possesses ideal facilities for such work. During the last five years these workers have gathered together a band of enthusiastic researchers, who have made valuable contributions to the subject under consideration.As a result of the investigations carried out at Cambridge and Vienna, our knowledge of the effects of a-bombardmeiit of the elements has reached a state which justifies the appearance of a monograph of the type under review. In writing it, the authors' aim was to arouse the interest of physicists in this fascinating branch of research, and to stimulate others to take an active part in its development. But, alas, the lack of strong radioactive preparations is a real difficulty. To those who are more fortunately placed in this respect, however, the book will be found of great value in making readily accessible not only the experimental methods and results, but also their interpretation. The number of substances so far investigated is relatively small, and the methods of attack used at Cambridge differ in many respects from those used at Vienna. In consequence, the results obtained in the two laboratories are not always directly comparable, and in some respects show lack of agreement. Nevertheless, the authors have endeavoured to be impartial in their treatment, and science owes them a debt of gratitude for presenting such an excellent review of the subject. In the opening chapter the question of transmutation in general is treated historically, and the authors wisely refrain from a discussion of recent claims in this field. We are then introduced to the main properties of a- and H-rays, and pass in review the relevant theory and the experiments carried out to test the validity of the nuclear theory of the atom. Chapter iii. deals with the earlier experiments on atomic disruption carried out at Cambridge and Vienna, and discusses the results of investigations on the a-particles of long range emitted by the (7-products of radium and thorium. By the introduction of the method of observation of the atomic fragments in a direction perpendicular to that of the bombarding a-particles, it became possible to count scintillations much nearer the source of disruption, for both the number and range of the scattered a-particles are greatly reduced in this way. This method has been successfully applied both at Cambridge and Vienna, and the various results are given in the same chapter. The res'ults of observations in the backward direction by the ' retrograde ' method are also described. This method has been extensively used at Vienna and permits of a still closer approach of the counting screen to the material under examination. The more recent investigations on collisions with the nuclei of atoms are reviewed in Chapter iv. Since the intensity of the scintillations produced by a-particles falls off considerably near the end of the range and the brightness of H-scintillations is much less than that of scintillations due to normal a-particles, the correct allocation of feeble scintillations is often a matter of difficulty. Pettersson and his co-workers have developed the technique of identification by direct comparison of a- and H-scintillations, and this is described in Chapter v., where an interesting account of the photographic action and absorption of H-particles is also given. This chapter also contains a description of Stetter's ingenious adaptation of the mass-spectrograph, by means of which the value ejm 9560 ±300 was found for the H-particles from paraffin wax. Chapter vi. is devoted to the various unsuccessful attempts which have been made from time to time to influence the rate of decay of radioactive substances, whilst the following chapter deals with various theoretical considerations on such topics as nuclear collisions and the size of the nucleus. For any one contemplating work on the subjects of this volume, Chapter viii. is a veritable mine of useful information. It contains most valuable details on the preparation of sources of radiation, the application of the scintillation method, the optical devices used in work on disruption, the preparation and calibration of absorption screens, and other matters of technique. The book closes with an interesting chronological review of the work on atomic disruption, and a complete list of the relevant references to the literature.Prom the results of the Vienna workers, the phenomenon of disruption by a-particles would appear to be of much more general applicability than the Cambridge results indicate. Moreover, whereas the latter school finds that disruption is not effected by a-particles of smaller range than about 4-9 cm., the former claims to have obtained positive results with a-particles of range less than 4 cm. (e.g. with polonium). The yield of H-particles found in Vienna is also considerably greater than that found at Cambridge. Such discrepancies do not appear surprising when we consider the great strain associated with the counting of such feeble oscintillations as those produced by H-particles, so clearly revealed on p. 225 of the book under review. It is unfortunate that observations have usually been made on the side of the scintillation screen remote from the zinc sulphide surface, as this must involve a distinct diminution in the brightness of the flashes, and render counting more difficult and less certain. Naturally, both schools have great faith in their own results, and whilst Kirsch and Pettersson have obtained evidence that the observed differences are attributable to the different optical arrangements used, Chadwick has directed attention to the difficulty of ensuring the absence of scattered a-particles of low velocity in experiments at short range. In our opinion, the position of the Viennese workers has been greatly strengthened by theirmore recent confirmatory evidence obtained by other methods, and it is to be hoped that before the appearance of a second edition of this valuable book the existing discrepancies will have been satisfactorily removed, and the main features of this fascinating subject firmly established

ISSN:0028-0836    

DOI:10.1038/120178a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

IT is becoming more and more realised that it is a matter of primary importance to the stock-breeding industry to possess an understanding of the processes of reproduction and development. Of our existing knowledge of this subject in its relation to the breeding of farm animals, some was acquired long since by direct practical experience and has been handed down for countless generations. It follows that such knowledge, although generally sound-for otherwise it could scarcely have stood the test of time-was necessarily limited and uncorrelatcd, for it existed without reference to scientific system and is not founded on scientific principles. In recent years, however, a great deal of attention has been paid to the science of breeding, and although it cannot be said that research methods have led as yet to any spectacular developments of economic importance, nevertheless a great number of observations have been made and deductions arrived at which in the aggregate arc already having an important effect upon practice. The present volume has been written as a textbook on the breeding and rearing of farm animals. While it is in many respects severely practical, the author has succeeded in giving it a definite scientific bias, and much of the recently acquired knowledge which has been won by physiological and genetic investigation is duly included. Moreover, by giving a connected account of the different departments of the subject, the author points the way to further progress in the improvement of the various classes of stock.The opening chapter, among other matters, deals with the derivation and history of the domestic animals, and the author, in common with other writers, takes the view that most of the species have had a multiple origin, but Prof. Ewart's extended researches on this subject are not alluded to. Chapter ii. is on the physical basis of inheritance, and the chromosome theory is adequately described. Here the author definitely identifies the genes or factors with the ' beads ' which comprise the chromosomes. In a later chapter he goes even further and suggests that the genes are either proteins or enzymes (or both), merely making the reservation that "it is not known " which of the alternatives is true. Such a statement is much too crude for a scientific text-book, and we fail to see what advantage is gained, in the present state of knowledge, for any theory of heredity by identifying the mechanisms of transmission with definite chemical compounds or agencies. The third and fourth chapters contain useful * descriptions of the male and female genital organs, and the processes which occur in them, but the almost complete absence of any account of the uestrous cycle is a strange omission in a text-book on animal breeding. Such information as is given is confused and contradictory. Thus, the author quotes Williams as saying that " if a cow is bred during a heat period and docs not conceive she will subsequently menstruate, while if she does conceive she will not menstruate." Here Williams's reference to ' menstruation ' was clearly intended to refer to the sanguineous discharge which sometimes takes place shortly after cestrus and really represents the termination of the preceding cestrous cycle. Prof. Rice, however, in the very next sentence proceeds to state that " the menstrual period lasts for about 24 to 48 hours in cattle," etc., and that " this is a most important season, because it is apparently only during this time . . . that a mare, cow, ewe, or sow can be successfully impregnated." The use of the term ' menstruation ' as synonymous with cestrus is quite unjustified.In the next chapter, on fertility, there is some further allusion to the oastrous periods (p. 54), but the distinction between the monoestrous and poly-(Bstrous conditions is not drawn and there is no reference whatever to the short (diosstrous) cycle either in pigs or sheep. This is also omitted in the summary of the " Chronological Order of Reproductive Processes " (p. 47), where we find a further confused statement as to menstruation (in cattle). Again, it is not correct to describe the absorption of the corpus luteum as occurring at a later stage of the cycle than "nutrition of young." It is a mistake also to describe the vasa deferentia as the homo-logues of the Ifallo'pian tubes, as these have a different origin in embryonic development. There is an interesting description of the American work on the vitality of the ova and the spermatozoa, but no account is given of Hammond's more extended investigations published in 1925, and the author does not appear to realise the practical possibilities of transmitting semen from a distance or the importance of. what has actually been accomplished. The succeeding chapters on sterility and reproductive efficiency deal with many matters of practical importance besides pointing the way to further lines of work. It is interesting to note that some of these (for example, the question ofthe time of ovulation in the mare) have already been taken up. The sections dealing with parturition, genetic problems, grading, inbreeding, etc., are also full of interest, and the analysis of the show-yard records of the leading animals of different breeds contains much information which is not otherwise readily accessible. The chapter upon the development of farm animals includes many useful hints as to management and feeding. The last chapter, entitled " Fitting for Sale and Selling," is entirely practical, and directs attention to sundry matters of importance to every breeder who would market his products successfully.The book is well illustrated, many of the figures being photographs of outstanding specimens of farm animals. There are appendices on biometry and inheritance in horses, cattle, etc., besides a list of Pedigree Register Associations and a bibliography of references. In the second edition, which ought soon to be called for, these should be made more complete and the results of the latest researches incorporated.

ISSN:0028-0836    

DOI:10.1038/120180a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

PROF. SPEARMAN'S new book, embracing his researches for some years past, is an exceedingly difficult book to review, and this for more than one reason. In the first place it is distinctly written for the layman, and he is expected to take many things on faith. He has to trust Prof. Spearman's mathematics and still more Prof. Spearman's arithmetic. Now we can scarcely call upon the author of a popular book of this nature to justify either arithmetically or mathematically all his statements, but we do think that without overcrowding his pages he might have given us more of the numerical data on which his conclusions are based, so that we could test their adequacy without an immense amount of labour. This point is all the more to be emphasised because Prof. Spearman claims to have made by his investigations a " Copernican revolution in point of view." He tells us that he has "not - as all others - set out from an ill-defined mental entity the ' intelligence ' and then sought to obtain a quantitative value characterisin this. Instead, we have started from a perfectly defined quantitative value ' g,' and then have demonstrated what mental entity or entities this really characterises " (p. 411). Now in order to test the justification for this* statement that a Copernican revolution has been made in the study of the human mind, it is certainly needful to check not only the arithmetic but also the mathematics on which the claim is based, and neither of these are light matters, especially in such a brief review as this must necessarily be. But without some reference to the mathematics of the subject the real basis if our author's Copernican revolution cannot be rendered clear, nor without some arithmetic can we determine whether the values he gives are to be accepted straight off.With much of the author's criticism of the definitions of intelligence hitherto proposed, we must undoubtedly agree; it is ably and amusingly written . But Prof. Spearman escapes any like criticism of himself by giving no definition of intelligence at all. He hypothecates that the measurement of a mental ability (An) is a function of two factors, a general factor g and a specific factor sn, the former being a factor of all a person's mental abilities and the latter varying from ability to ability, g is independent of the sn's, and the latter are independent of each other. Mathematically where £ is a function as yet undetermined. Prof. Spearman then proceeds to replace this general functional relation by a purely linear one; he in fact writes and all his conditions and his treatment depend on this linearity. Now the mind is a complicated organism, and quite as complicated as many physical phenomena, which do not obey any such linear relationship. What real justification is there for the adoption of such a form? " The answer to this question is that our proof has depended upon usage of Taylor's theorem, according to which all mathematical functions, however complex, can, in general, be expressed in the above simple additive form with some approximation. This theorem has supplied the main foundation for the whole theory of correlation, from the original work of Bravais onwards; indeed, it is among the main props even of physics " (p. xv, Appendix).We do not know how many physicists would agree with such a statement, but we presume that if they have adopted a linear relation, it is because it has been demonstrated experimentally to hold within some limited range. In the same way the only justification for linearity of regression is not Taylor's theorem, but observation and experiment. With our knowledge of the innumerable cases in which regression is non-linear, it is neither possible to assert that linearity is the main foundation of the whole theory of correlation, nor to accept it without foundation on experiment as a justification. Some light might have been thrown on the matter had Prof. Spearman provided a distribution of g's for a population of reasonable size. Accepting for the time this linear relationship, what flows from it? Without doubt, if a, b, c, d are four measurable abilities, the vanishing of what Prof. Spearman terms their tetrad differences, i.e.:V V, - V,1 ' "e' [id ' ridOf course, in actual statistics this vanishing will depend upon the error of random sampling of a tetrad, and ultimately this error depends on the number (p) of individuals on which the correlations have been based. When p is small and the correlation r is large, the distribution of r does not follow the normal curve of errors; it is very far indeed from doing so. Correlations as high as 0-60 based upon 37 individuals deviate widely from the normal law, and many such occur in the chapter entitled " Proof that G and S exist." But whether the distribution of correlations be normal or not, it is perfectly certain on the basis of Prof. Spearman's own data that the distribution of tetrads is not normal. What it really is, even if the original mental ability correlations followed a normal law, no one at present knows. We are simply ignorant, and it is impossible to consider that any confirmation of the theory of two factors can be reached by placing a normal curve on top of the distribution of tetrads and judging merely by the eye of the goodness of fit. For example, the most ample data discussed by Prof. Spearman are those of TTolzinger, involving 378 tetrads, and those of Simpson involving 3003 tetrads. If we apply to these distributions the normal curves for the theoretical standard deviations of these systems of tetrads, i.e. the actual values, not those computed by the approximate formula of Holzinger and Spearman from the mean correlation, we find for the first distribution, only one random sample in ten would be as bad a fit to the normal curve, and again for the second, that not one random sample in a million would give as bad a fit. Now we do not complain of these distributions failing to be normal curves, because we hold that they ought not to be. But we do complain of Prof. Spearman assuming them to be normal distributions, and using this as an argument in favour of his two-factor hypothesis. Indeed, after placing a normal curve on his data in the last case, Prof. Spearman writes (p. 146): " This time, the two distributions, curve and rectangles, far from being totally discrepant as before, display instead one of the most striking agreements between theory and observation ever recorded in psychology. Indeed, it would not be easily matched in any other science."These words seem unfortunate not only because of the high improbability of the curve fitting the data, but also because there exists no theoretical reason why it should do so. Prof. Spearman starts with rendering his distribution of tetrads symmetrical, i.e.. making each tetrad once positive and once negative. Hence he naturally has something that looks like the familiar cocked hat shape of the curve of errors. Further, he can in this manner reach no test whatever of whether they are zero within the limit of random sampling. He has made his mean tetrad difference value zero artificially. For Simpson's data the diagram has attached to it a scale lettering, in which 0-020, 0-030, 0-035 are printed where we ought to have 0-20, 0-30,and 0-35, that is, the tetrad differences are accidentally, but very unfortunately, given one-tenth of their true values, and accordingly appear very small. Underneath the diagram we read: Probable error =0-061, Observed median = 0-062. This latter is the only real test provided of the agreement of theory and observation. It is not quite clear how Prof. Spearman has obtained these figures. The actual theoretical mean value of the 3003 squared tetrads is 0-007,887 corresponding to a theoretical standard deviation of 0-088,809, or if we use the term probable error, although the distribution is not normal, we have the value 0-059,901 instead of Prof, Spearman's 0-061. If we understand by Observed median, the observed quartile of the symmetrical tetrad difference distribution, it is 0-0581, not 0-062 as given on p. 146. The question would then be whether 0-060 and 0-058 are in good agreement. But a bettr way to approach the problem is probably to note that the theoretical mean squared tetrad is 0-007,887, while the observed value is 0-009,817. The difference between observed and theoretical mean is thus 0-001,930. If we could measure the probable error of the mean in the usual way on 3003 observations with a standard deviation of 0-017,769, it would be 0-000,219, or the deviation would be some 8-8 times the probable error. We should accordingly conclude on these data that the new Copernican theory, so far from being in "striking agreement" with observation, signally failed^ While, however, we know the theoretical mean squared tetrad value-always, alas ! on the basis of variates following a normal distribution-we do not know the true probable error of this squared tetrad value. The reason for this is that the tetrads are not like the individuals of an ordinary frequency distribution merely correlated by the fact that the size of the sample is fixed. On the contrary, there is correlation produced by the fact that in this case the 3003 tetrads are functions of only 91 individual correlations, and this correlation is very high in the case of the triplet of tetrads based upon sets of four correlations. To determine the true probable error of the sum of the squared tetrads will be a problem which will task the ablest mathematician, even if he assumes (i) £hat the original mental variates follow the normal law and (ii) that the correlation coefficients follow-which we know they do not- the same law. At present no one can say whether or not the sum of the squared tetrads differs from its theoretical value by amounts which can be accounted for on the basis of random sampling. But we can say that what Prof. Spearman considers proofs of his theory are not proofs, and that much mathematical work remains to be done before we shall even be in sight of a proof. With the failure of Chapter x., that is, " Proof that G and S exist," the very backbone disappears from the body of Prof. Spearman's work. Even if the correlations of mental abilities were taken to vary at random with a given standard deviation round a given mean, the distribution of the resulting tetrads would form an approximately normal system, and many tetrads would vanish or nearly vanish; it would be idle to pick these out as special illustrations of g. But this is in fact what occurs in the later chapters of " The Abilities of Man."We have confined our criticisms to one point: there are others, especially in the mathematical appendix, where we hold Prof. Spearman's analysis to be defective. But it seems to us that there is one main question: Is the experimental proof of the existence of a general and of specific factors on which the author bases his discussions in this work valid? Prof. Spearman holds that it is; we hold that it is not. The truth can only be ascertained by lengthy arithmetical and mathematical investigations, unsuited to a review of the present kind. One advantage of the publication of this book will be that the attention of mathematicians will be directed to the real difficulties of the analysis, and this should lead, in conjunction with the psychologists, to a fitting series of tests in which probably some fifteen to twenty abilities should be measured on four or five hundred individuals. In particular, the abilities must be selected beforehand, and none rejected after analysis because they do not satisfy the condition of zero tetrad difference. Prof. Spearman has had the merit of directing attention to the subject, but his book will do more harm than good if it leads the non-mathematical psychologist to believe that the author has proved his hypothesis. It may possibly turn out to be true, but the proof will have to be far more rigid than anything so far provided in " The Abilities of Man.

ISSN:0028-0836    

DOI:10.1038/120181a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

THESE two volumes deal with two different aspects of the exploitation of central Africa. Mr. Barns is chiefly concerned with the development of the mineral and agricultural resources of the Congo basin, particularly those parts under Belgian control; Miss de Watteville sees tropical Africa through the eyes of a naturalist. Mr. Barns paints an illuminating picture of the fertility of tropical soil, the scope for the development of the wealth of its natural vegetation, its metalliferous ores and precious stones, and indicates the respective roles of the white man and the native in this development. Miss de Watteville's only concern is the exploitation of the fauna of the tropics in the interest of the Berne museum, by the authorities of which she arid her father, the late Bernard de Watteville, were commissioned. Within the compass of 225 pages Mr. Barns deals with most of those aspects of African life and travel which interest most of us, whatever our peculiar interest may be, whether geology, botany, zoology, history, or anthropology. Miss de Watteville devotes the same amount of space to a straight tale of systematic killing of wild animals and the preparation and preservation of their hides for a museum. Lingering yet in our memory is the account given by the late E. D. Morel of the horrors of the Leopold regime in the Congo, an account which aroused the peoples of Europe to effective protest. Now, according to Mr. Barns, Belgian administration in the Congo is characterised by as much regard for the welfare and progress of the natives as the British administration in West Africa. Sir Louis Pranck, former Belgian Colonial Minister, who contributes a preface, describes the official attitude thus: " We believe in the progress and future of the black man, and we want to pave the way for him towards a better standard of life, a great improvement in health and efficiency, and a higher civilisation. . . . We are absolutely opposed to anything like colour bar or race discrimination in the opportunities offered to black labour."The difficulties of the Belgian administrators are common to all aliens in tropical Africa. They are faced with great difficulties of communication which the mighty waterways do not altogether surmount, with multitudinous insect pests-a constant menace to man and beast-the conservatism of the natives, the diversity of tribes and languages, pygmies in close proximity to giants, and the shortage of capital. On the other hand, they have certain special advantages. "All its eggs are in one basket." The upturned edges of the basin of the Congo are a storehouse of mineral wealth in amazing abundance, while in the well-watered plains the oil-palm, rubber, rice, cotton, sisal, and other economic plants nourish, and there is rich pasturage for cattle on the slopes of the basin. In the south there are mountains of copper in the Katanga Copper Belt, with gold, tin, radium, and cobalt in close juxtaposition. In the Mandated Territory of Ruanda, on the east of the Rift Divide, is one of the most populous and richest cattle countries in Africa, the cattle possessing the advantage of immunity from East Coast fever. In the north-east are the Kilo and Moto gold mines, and again to the south, in the Kasai, extensive diamond fields are being worked. On the material side, therefore, Mr. Barns regards the Belgian Congo as "an Eldorado," a country which promises a rich return for men of small means as well as for development companies with large financial resources. The main interest of this arresting volume lies, however, not so much in the author's description of the material resources of the country, as in his description of the scenery, of the peoples, their habits and customs, their arts and crafts, of the flora and fauna, and his incidental notes, some of which arc of particular interest to scientific workers. For example, in the high country in the Kivu craterland, there are no tsetse-fly, but the cattle suffer from tsetse-fly disease. In the fly-districts around Lake Edward and along the Semliki river, man and his domesticated live-stock have managed to hold their own against the epidemics of nagana and sleeping - sickness that have so often ravaged the district. The African elephant, he tells us, " is very free from disease, can thrive at all elevations from the sea to 13,000 feet (the equatorial snow-line), can stand alike either cold or heat and can obtain nourishment from a greater variety of vegetation than any other animal." Mr. Barns's book, with its beautiful photographs, will add to his already considerable reputation as a charming and accurate observer of the Africa he loves.To those who are interested in the details of a ' collecting ' expedition, and wish at the same time to read an amazing story of a girl's pluck and persistence after the tragic death of her father in an encounter with a lion, Miss de Watteville's book can be recommended.

ISSN:0028-0836    

DOI:10.1038/120183a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

THIS volume is divided into two sections, dealing respectively with the natural and the synthetic resins. Perusal of the former of these sections gives the impression, only too correct, that our knowledge of the chemistry of the natural resins consists mainly of information concerning botanical sources, methods of collection, and of a few variable ' constants.' Practically only in the case of colophony, the commonest resin, has any approach been made towards elucidation of the chemical constitution of complex bodies present in these natural products; it is not surprising, therefore, that the author has allotted to this particular topic one-third of the space in this section. Following a brief account of the botanical origin and nature of resins by Dr. Willis, the first two chapters deal with general physical and chemical properties. Only resins of interest to the varnish maker are considered, and these are classified under the following headings: hard and semi-hard resins, spirit-varnish resins, colophony, soft resins, true lacquer, and shellac.Despite systematic attempts at the conservation of sources of supply, the partial exhaustion of the natural resin constitutes a danger which should not be overlooked; the introduction of the synthetic resins, therefore, is most timely. Although our knowledge of the chemical processes involved has lagged behind the technical side of the subject, investigations during the last few years have afforded considerable insight into the various causes and stages of resinification; these are well set out in the volume under notice. The synthetic resins, other than those obtained by treatment of the natural varieties (e.g. by esterifica-tion of colophony and copal) which are also dealt with in this section, fall broadly into two classes, the condensation resins and the polymerisation resins. These are considered under their respective headings; other products, such as the treated phenol-formaldehyde resins and those from urea and thiourea, are considered separately. The section concludes with a brief chapter on the methods of testing synthetic resins. The book covers a very large field, and certainly presents in modest bulk a useful summary of our present knowledge of the products discussed. The index is adequate, although one or two omissions have been noted. Unfortunately there is an unduly large proportion of misprints, mainly in the first section; names mis-spelled in the text persist in the index, whilst some references are incorrect.

ISSN:0028-0836    

DOI:10.1038/120184a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

DURING recent years considerable progress has been made in the description of ferriferous sediments. Works by Hayes on the Wabana iron ore (1915), by Cayeux on the French secondary ores (1922), and by Slavik on the Czechoslovakian deposits have contributed substantially to the elucidation of the chamosite-bearing rocks, while corresponding researches have been carried out on the English iron ores by the Geological Survey of Great Britain since 1920 (see " Summary of Progress for 1922 " (1923), and Special Reports, vol. 29 (1925)). The present work contains a review of this question on similar lines to the above, dealing in some detail with the German deposits. The author limits himself to the discussion of existing literature on the subject, with a few additional descriptions, and provides a useful account of many rather inaccessible papers on local ores. In dealing with general literature the author has evidently been somewhat at a disadvantage, for of the works above mentioned not one appears in the bibliography, though there is passing reference in the text to the report by Hayes. The views advanced are substantially in agreement with those generally current, the ores being regarded as primary sediments. Interesting sketches are given of the tubular organisms sometimes found in the ooliths; the author does not regard them as having played an essential part in the formation of the oolith, but rather as parasitic growths accidentally preserved in the inorganic structure. Chamosite is described in detail from the mineralogical viewpoint, but the corresponding account of glauconite is scarcely adequate, and more space might perhaps have been given to the discussion of the glauconitic sediments. As is perhaps inevitable in a work of compilation, the tone of the discussion appears somewhat speculative, for the origin of these rocks has been the subject of a great variety of conflicting theories; but many useful observations are recorded. The microstructures are illustrated by twelve photographs of chamositio sandstones and oolitic ores from French, Belgian, and German localities.

ISSN:0028-0836    

DOI:10.1038/120185b0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

THE parts of Gmelin's new " Handbuch " which deal with lithium and bismuth, like the earlier parts, show abundant evidence that a painstaking and exhaustive review of the literature up to July 1926 has been made. Following the general plan of the work, the parts open with notes on the history and distribution of the elements. Then follows a comprehensive survey of their physical, electrochemical, and chemical properties, and a similar scheme is adopted in dealing with compounds of these elements with such other elements as precede them in the scheme (see NATTJRE, Mar. 5, p. 346). That the search through the literature has been thorough may be inferred from the fact that the description of one salt alone (lithium chloride) occupies fifty pages and contains detailed numerical data relating to hydrates, to solutions in water and in organic solvents and to complex ammine-chlorides. A summary of recent work on the atomic dimensions, atomic structure, and isotopes of lithium is given, whilst the radioactive isotopes of bismuth are fully described in a special section, which includes not only detailed references to recent papers but also a synopsis of the general literature on the subject.

ISSN:0028-0836    

DOI:10.1038/120186b0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

THE more important agencies which may conceivably cause the ionisation of the upper atmosphere of the earth are the ultra-violet light, α- and β-particles, all of solar origin, the penetrating radiation of cosmic origin, and the ionising radiations from terrestrial sources. The last mentioned may perhaps be ruled out immediately because of the fact that the conductivity of the lower atmospheric strata increases rapidly with the height for the first few kilometres. The possible effects of these ionising agencies have been considered in papers by Chapman and Milne, Benndorf, Elias, Lassen, and others. Recently, experiments with the electromagnetic waves of wireless telegraphy, together with theories of the propagation of these waves over the surface of the earth, have led to more definite information about the ionisation in the upper atmosphere, and it has been of interest to examine again the causes of the ionisation.The experiments of Breit and Tuve with 70 metre waves, of Heising with 57 and 111 metre waves, of Wagner and Quack with 15 and 16 me£re waves, and the experiments of Taylor on the skip distances of waves below 50 metres and the theoretical considerations of Taylor and Hulburt of these skip distances, show that the electron density N increases with the height Z above the earth, reaching a value of about 4 x 105; above the height where N has this value, nothing is known of the electron density except that it does not go on increasing. Although the wireless data are none too extensive, it may be taken that in summer (for the north temperate zone) the height where N is of the order 105 is roughly 150 km. at midday, rising to 300 km. at 2 A.M., and in winter is around 200 km. at midday and 600 km. at night. To this may be added ah interpretation from the experiments of Appleton with 400 metre waves that N is of the order of 103 at about 100 km. for a June night in England. Because of the diurnal variation in the ionisation, we chose the ultra-violet light of the sun as being the ionising agency deserving first consideration. In order to make an explicit calculation of the ionisation of the temperature, the pressure, and the constituent gases and their partial pressures, must be known at each height in the upper atmosphere. These we may take as given completely in the classical thermo-dynamic isothermal equilibrium theory of Humphreys, Jeans, and others. There is a question as to the existence of hydrogen in the upper atmosphere, but the conclusions given later are much the same whether hydrogen is there or not. There is also the question of ozone, or oxygen, which may be of great importance.Further, the law of the recombination of the electrons with the positive ions must be known. When the electron collides with a positive ion, in order for recombination to occur, energy must be dissipated in some way, either (a) by a third body, such as another molecule-this is J. J. Thomson's theory of recombination, and complete formulae are available-or (6) by radiation (simple formulae for this case are easily derived). We must also recognise the possibility of the electron attaching itself to a neutral molecule, for when it does this, thereby producing a negative ion, it is no longer as energetic a refractor of the wire-less rays. The oxygen molecule is the only important one in this connexion, and the values of the attachment coefficient measured in the laboratory for pressures of 10 mm. of mercury and above must be extrapolated to pressures below 10~2 mm., perhaps a questionable extrapolation. Using all these things with (a) and making entirely acceptable assumptions as to the amount of ultra-violet light from the sun in the spectral region useful for ionisation, the N, Z curve rises rapidly from N = 0 at Z - 100 km. to N = 4 x 105 at Z = 150 km.; above this height N falls off slowly. With (6) the N, Z curve is much the same as with (a), but N falls off more rapidly with Z above 200 km. Either of these N, Z curves is in fair accord with the wireless data for full daylight conditions. One might be content with the agreement, for the present, were it not for what happens at night. At night, after the removal of the sun's ultra-violet radiations, the calculated N, Z curve sinks down somewhat towards the Z axis, but with no great change in the height at which N rises to 4 x 105. This is distinctly contrary to the indications of the nighttime wireless data, which require the electron bank to move up, so that the height at which ^ = 4 x 105 at midnight may be roughly twice the midday height. In an endeavour to bring the calculations into accord with the wireless experiments, we may abandon the classical pressures, increasing them by a factor of 102 or 103 for heights above, say, 150 km., and at the same time increasing the partial pressure of the oxygen at these heights. In this way we can obtain the electronic densities at night and day required by the data of the shorter wireless waves. In increasing the classical pressures we are doing exactly what Lindemann was led to do in his theories of the meteors. He has suggested that the formation of ozone, with its attendant strong absorption from 2000 A.U. to 3000 A.U., may be a sufficient cause of temperatures and pressures higher than the classical ones. The existence of oxygen in the higher levels is supported to some extent by the recent identification of the auroral line with oxygen. There remains, however, a difficulty with the 400 metre waves of Appleton. A simple smooth increase of the total gas pressure and the partial oxygen pressure, which yields an ionisation satisfactory for the shorter waves, wipes out the night-time ionisation below Z = 130 km.A way out is to assume an irregularity in the pressure-height curve; for example, to assume that the pressure drops off with the height, then increases to a maximum at 80 km. or 100 km., and decreases thereafter. Or, one may assume an ozone layer at this height and that the ozone does something peculiar to the ionisation, such as disintegrating slowly to oxygen during the night, thereby in some way maintaining the ionisation. Chapman has pointed out this possibility. Further, one may put aside hypotheses of the kind just mentioned and assume that the pressures of the constituent gases of the upper atmosphere are those of the classical calculation and that other agencies of ionisation exist besides the ultra-violet light, which are effective by night as well as by day. It seems that such a view meets with no immediate objections. For example, the number of a -particles from the sun necessary to produce the desired ionisation, if they are similar to those of radium-(7, requires a small and quite permissible amount of radium at the solar surface. One can speak less definitely of,8-particles of solar origin and of cosmic radiation. In a final summing up one may have to reckon with all of these possibiliti

ISSN:0028-0836    

DOI:10.1038/120187a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature

摘要:

As has been discovered by Compton1, X-rays falling on a polished surface at small glancing angles are totally—or at least nearly totally—reflected. This phenomenon was explained by Compton as being due to the fact that the index of refraction of X-rays is a littlelessthan unity:n=1−δ, where δ is small compared2with unity.Indeed, applying Fresnel's well-known expression for the intensity of reflection, we find in this case for small glancing angles the formula 1r=102for the fraction of the incident energy which is reflected. A graph of this function (for 23 = 6 x 10~6) is given in Fig. 1 (curve A); it shows that below a certain critical angle 00, given by 00 = \/2$, the reflection is total, whereas for angles>9^ the reflecting power falls down rapidly. Since its discovery the phenomenon has been studied by several authors, but so far as T know it lias not occurred to any one of them that this theory needs some extension in so far as the absorption has also a considerable influence on the reflection. According to elementary wave-theory we may take this into account 3 by putting in Fresnel's formula the complex value n: 1 - S + d for the index of refraction, where 2$ is the absorption coefficient (for the energy) taken for l/2ir times one wave-length. Instead of (1) we then get;I,. (2) - 2S~+2ci-This function is given in the curves 73 and C of Fig. 1. The values taken for the constants, 28= 6 x 10"5, 2e = 0-2 x.lO-6, and 1-5 x 10"6 Correspond to the reflection by iron of wave-lengths a little greater and a little smaller than 1740 X.U., this being the wave-length of the K-absorption discontinuity of iron.I have performed some experiments showing the dependence of the reflection upon the absorption in a marked manner. The device used was a very simple One. Two identical rectangular mirrors of stainless steel4 were put together, their optically polished surfaces confronting each other. These surfaces were kept parallel and at a distance of 50/j. apart from each other by putting small pieces of aluminium leaf between them at the four corners. The ' slit ' so formed was then put horizontally between the focal spot of an X-ray tube and the vertical slit of an X-ray spectrograph-the method being not unlike the ' method of crossed prisms ' in optics.Fig. 2 is a reproduction of a photograph obtained in this way (tungsten target; exposure 20 hours); it contains the spectral region on both sides of the ^f-absorption discontinuity of iron (X = 1740 X.U.). If there were no such phenomenon as reflection against the steel plates, we should have obtained a spectrum of exceedingly short lines the height of which would be determined by the distance between the steel plates. Owing to the reflection against these plates the lines are much higher, their intensity in vertical direction giving a measure of the reflecting power of the' stool at the corresponding angle. A complication is introduced by the fact that the radiation corresponding to relatiyely great angles is repeatedly reflected at the plates before leaving the ' slit.' Fortunately, the number of reflections is recorded on tho plato by the horizontal strife (these stride being due to irregularities at the edge of the plates). If we wish to compare the distribution of intensity in vertical direction with the theoretical curves B and C, this influence may be taken into account. When this is done, the agreement between theory and experiment is sufficient, the limit of visible blackening corresponding to a little less than the angle for which, according to theory, the intensity should bo reduced to half its initial value.FIG. 1. - Theoretical curves for the reflecting power of iron for X-rays as a function of tho glancing angle fln the figure Q stands for): A, when the absorption is neglected; -B, with weak absorption (long wave-length sid" of It -absorption discontinuity); C, with strong absorption (short wave-length side). So far we have considered only the influence of tho wave -length on the reflection caiised by a change of e (formula (2)). The quantity S, however, also changes with the wave-length. If we look apart from tho neigh-bourhood of the absorption-edge, this should cause the ' critical angle ' of reflection (in our experiment the height of the spectrum) to be proportional to the wave-length. This has been verified already by Compton, and is confirmed by my experiments (covering spectral regions from 0-5 A.U. to 2 A.U.), with considerable accuracy.FlG. 2.-Photograph showing the reflecting power of iron for X-rays on both sides of the K-absorption discontinuity: 1675 = \V LI; 174(>= Fe -K-abs.; 1753 = Fe Kfa. In the immediate neighbourhood5 of the discontinuity, however, we should expect a decrease of the height of the spectrum, the rate of this decrease being particularly large quite near to the edge. Whether such a phenomenon exists or not is a question which our experiments as yet are not able to settle; but it is hoped to get evidence on this point in the near future.8In conclusion, I wish to thank Prof. Coster and Prof. Kramers for the kind interest they have shown in this investigation. The mirrors were supplied by Messrs. Ottway and Co.,

ISSN:0028-0836    

DOI:10.1038/120188a0

出版商:Nature Publishing Group    

年代:1927

数据来源: Nature