摘要:

The American Geophysical Union has to do with those theoretical and applied sciences relating to the Earth, its configuration, its structure, and the natural forces acting upon and within it. Since the founding of the Union in 1919, it has gradually developed so that in 1952, with nearly 5000 members, it is perhaps the principal organization in the United States of America acting as a clearing house for new scientific thoughts and ideas relating to Geophysics.Sponsored by the National Research Council of the National Academy of Sciences, the Executive Committee of the Union is the Committee on Geophysics of the Council and the National Committee for the United States of America of the International Union of Geodesy and Geophysics.The wide‐spread special interests of the eight Sections of the Union are expressed in papers presented at the annual meetings, in the regional meetings (often held in cooperation with other scientific organizations), and in the Union's Transactions, which were formerly published annually and published bimonthly since 1945. Symposia on timely subjects are annual features of the General AssembliesThe fields of the Sections of the Union are: (a) Geodesy; (b) Seismology; (c) Meteorology; (d) Terrestrial Magnetism and Electricity; (e) Oceanography; (f) Volcanology; (g) Hydrology; and (h) Tectonophysics.The American Geophysical Union has made every endeavor in the past 33 years to increase coordination and collaboration of interests, both nationally and internationally, and to maintain continuity of the functions of the International Union of Geodesy and Geophysics, thus protecting for future international activities those relations so essential to geophysical investigations, especially during World War II. A prominent Geophysicist of California has said: “The Union, in my opinion, is to be congratulated for having the vision and courage to proceed (during the War) with the annual meetings. The Nation needs more, not less, scientific endeavor.”In these chaotic days following World War II, as never before, responsibility for continued attainment of geophysical knowledge falls with particular emphasis upon the Geophysicists of the Western Hemisphere. Now, as never before, American scientists personally benefit by affiliation with their fellow scientists and co‐workers, since the individual worker is under a great handicap. Now, as never before, scientists in general of the Western Hemisphere need to affiliate and play their part not only in the immediate problems of application, in which the Geophysicist is contributing effectively, but in the rehabilitation of international relations and endeavors particularly vital to investigations of the Earth sciences.This article must be limited to a general account of the origin and development of the Union during the 33 years from 1919 to June, 1952. As a matter of record, detailed particulars of the Union's history are given in the Appendices on subjects as indicated in the Table of C

ISSN:0002-8606    

DOI:10.1029/TR035i001p00005

年代:1954

数据来源: WILEY

摘要:

The work of the geologist and geophysicist has much in common with that of the physician. The work of both groups of men deals with a living body of which only the surface and such processes as are active on it are visible. Both want to know what goes on within, but must be content to base their diagnoses on indirect evidence. Both deal with the baffling complexity of unabstracted reality and look with envy on the basic sciences which achieve precision by lopping off all but the one process or property they are exploring. Both must go to the basic sciences for the understanding of what they observe, and both need men who bridge the gap between the concrete phenomena and the abstract processes ‐ geophysicists and geochemists on the one hand and biophysicists and biochemists on the othe

ISSN:0002-8606    

DOI:10.1029/TR035i001p00048

年代:1954

数据来源: WILEY

摘要:

The modern view of the origin of the geomagnetic field associates it with motions in the liquid core of the Earth. This new approach, suggested by W. Elsasser, hasled to a revival of interest in the main geomagnetic field and phenomena connected with it. The hypothesis of motions in the Earth's core not only accounts for the remarkably rapid changes in the geomagnetic field but also for the irregular fluctuations in the rate of rotation of the Earth.E. C. Bullard has given convincing arguments for the belief that these motions in the Earth's core arise from thermal convection. It may easily be demonstrated that the motions are to a high degree dominated by the Coriolis forces arising from the Earth's rotation. Consequently model experiments on thermal convection under the influence of Coriolis forces are of great importance in understanding the physics of the Earth's core. Such experiments, done by R. Hide of the Department of Geodesy and Geophysics of Cambridge University, give rise to an interesting explanation of the westerly drift of the geomagnetic field, discovered by E. H. Vestine, and give patterns of motion involving jet streams, which are incidentally of remarkable similarity to the motions in the upper atmosphere.The essentially two‐dimensional motions which result from the dominance of the Coriolis forces are thought to supply a fundamental reason for the axial character of the geomagnetic field. Though much is known about the physical processes in the core relating to the geomagnetic field, the mechanisms by which these motions set up electromotive forces are still obscure, though two lines of approach look promising. The first is that the motions maintain the field by a dynamo action and the second is that they set up temperature distributions which give rise to thermoelectric current

ISSN:0002-8606    

DOI:10.1029/TR035i001p00049

年代:1954

数据来源: WILEY

摘要:

The principal facts contributing to modern ideas of the structure of the mantle will be briefly reviewed. Particular attention will be given to the problem of a physical interpretation of the seismic velocities and their variations with depth, following a method discussed in detail in a recent paper by the author in the Journal of Geophysical Research (Elasticity and constitution of the Earth's interior). The principal conclusions are (1) that the mantle as a whole is not homogeneous; (2) that there may be a reasonably homogeneous layer between the depths of 900 and 2900 km, consisting of high‐pressure phases, presumably of the composition of a ferromagnesian silicate; (3) that gradual changes of composition of the proportion of high pressure phases, or both, take place in a transitional layer between the depths of 200 to 900 km. Discovery of the nature of this transitional layer is considered to be of crucial importance for dynamical geology and petrolog

ISSN:0002-8606    

DOI:10.1029/TR035i001p00079

年代:1954

数据来源: WILEY

摘要:

On the assumption that convection is an effective process of heat transfer in the mantle, petrological evidence suggests that the temperature at the core boundary fluctuates, in space and time, between a lower limit of about 1500°C and an upper limit of 2500°C. Generation of basaltic magma in the upper 100 km of the mantle is readily explained if the temperature gradient required to start convection does not exceed 0.6°/km, which is about twice the adiabatic value. Formation of uncommon magma types, such as anorthosites, may perhaps be explained by relatively small and momentary departures from conditions described. Implications of the convection hypothesis on the density distribution in the mantle are briefly discuss

ISSN:0002-8606    

DOI:10.1029/TR035i001p00085

年代:1954

数据来源: WILEY

摘要:

In 1947, the Finnish Geodetic Institute sent two expeditions to observe the total solar eclipse; one to Brazil, the other to the Gold Coast. The purpose of the expeditions was to determine the distance between the observation points through observation of the moments when the shadow of the Moon passes the observation points. These expeditions used specially constructed cameras which had been designed for solar eclipse recordings and featured a smoothly moving film (as contrasted to the jerky movement of film in commercial camera). Both expeditions were successful. The evaluation of their films gave the distance between two observation places with an accuracy of ±94 m. This error was mainly due to the prevailing poor knowledge of the profile of the Moon. When better values for the profile are available, it is expected that the error will be reduced to about half its present size

ISSN:0002-8606    

DOI:10.1029/TR035i001p00099

年代:1954

数据来源: WILEY

摘要:

The effects of the cosmic radiation in building up and altering the terrestrial isotope distribution are computed. The most striking effect is the production of radiocarbon, but as this beta‐decays to nitrogen it does not alter the distribution permanently. The second important process is the production of tritium, and its subsequent decay into helium three. The problem is discussed quantitatively. Finally it is shown that several other possible reactions do not contribute in an important degree to the existing distributio

ISSN:0002-8606    

DOI:10.1029/TR035i001p00103

年代:1954

数据来源: WILEY

摘要:

Nitrogen negative and second positive band spectra have been excited by 100‐kv protons and hydrogen atoms from the Rice Institute van de Graaff accelerator. The intensity distributions in the vibrational bands are compared with spectra produced in controlled laboratory experiments by canal rays and electron impact, with auroral spectra, and with results of theoretical calculations. Excitation of second positive bands by high‐energy neutral hydrogen atoms and of the negative bands by both neutral hydrogen and protons show the expected marked increase in the rate of population of high vibrational states. Theories for the excitation of the auroral bands are discussed in the light of these results and of theoretical considerati

ISSN:0002-8606    

DOI:10.1029/TR035i001p00107

年代:1954

数据来源: WILEY

摘要:

An analysis of the accelerating forces available within a relatively wide shallow channel bend shows that the existence of higher velocities near the outside bank requires, in addition to the helical flow pattern commonly observed, that the outward flowing upper layers be unaffected by bed shear. Velocity measurements made in a model channel bend at a point unaffected by entry conditions have confirmed this requirement, indicating that the inward flowing bottom layers move within a boundary layer similar to those found near the surface of airfoils. The parameter (r/v) dv/dr, which should have the value −1 for free vortex flow and +1 for flow with constant angular velocity, exceeded +4 in these experiments and was found to be directly proportional to the friction factor. Theory developed indicates that this parameter is directly proportional to the width‐radius ratio also in those regions beyond the effect of entry conditi

ISSN:0002-8606    

DOI:10.1029/TR035i001p00114

年代:1954

数据来源: WILEY

摘要:

It is shown that the non‐homogeneous case of soil‐heat conduction, that is, when soil‐heat conductivity and capacity are functions of depth, can be treated rigorously. An exact formula is derived which gives the thermal diffusivity of the soil as a function of depth, on the basis of Fourier coefficients of diurnal courses of soil temperature at a variety of depths. By employment of the new model of soil‐heat diffusion one avoids misleading results which are obtained when the classical model of heat diffusion in a solid conductor is applied to natural soil indiscriminately.The case of depth‐time varying thermal diffusivity can only be solved in approximate form. The practical application of the classical and the two new models is discussed with the aid of soil‐temperature data obtained by the Johns Hopkins Laboratory of Climatology, Se

ISSN:0002-8606    

DOI:10.1029/TR035i001p00121

年代:1954

数据来源: WILEY