ALBERT

Notes: It is suggested that the coincidence of the period of rotation of the Earth and a natural period of vibration of the atmosphere is not fortuitous but due to the Earth being driven at a constant rate in synchronism with the vibration. An observation by Kelvin that the gravitational couple on the atmospheric tides accelerates the Earth's rotation is recalled, and the production of mechanical energy to balance the dissipation of the oceanic tides is discussed. The astronomical evidence supporting the current view that the rotation is being steadily retarded is reviewed and found to contain contradictions, and it is claimed that the high value of the angular momentum of the Earth-Moon orbit supports the hypothesis of equilibrium.

Notes: Astronomical observations have indicated that variations in the Earth's rotation by several parts per hundred million sometimes occur over periods of one or two decades. These irregularities may be caused by variations in the distribution of matter, or by variable motion relative to the Earth. It is found that processes in the atmosphere and ocean are inadequate to account for all of the observed irregularities, but that their effect is not necessarily negligible. Processes in the crust and mantle could barely do so, but such processes seem highly unlikely for a number of reasons. The irregularities can be accounted for by a variable motion in the core amounting to a fraction of the total motion indicated by the westward drift of the Earth's magnetic field.

Notes: An extensive network of gravimeter stations has been observed by the Geological Survey of Great Britain using a Frost gravimeter. In the course of this survey gravimeter observations were made at recent pendulum stations in York, Newcastle-upon-Tyne, Edinburgh and Aberdeen. At these stations the gravimeter determinations gave values for differences in gravity from Pendulum House, Cambridge, which were consistent with the pendulum observations of Browne, Cook, McCarthy and Parasnis (1950). If the value of gravity at Pendulum House, Cambridge, is assumed to be 981.26500 cm/s2 the values at the other stations are found by combining the pendulum and gravimeter observations as:–York, Minster Crypt 981.41474 cm/s2± 0.00011Newcastle, King's College 981.50608 cm/s2± 0.00012Edinburgh, Royal Observatory 981.58014 cm/s2± 0.00013Aberdeen, Marischal College 981.69597 cm/s2± 0.00014From the observations at these pendulum stations an accurate calibration factor was obtained for the Frost gravimeter and this was found to differ significantly from the calibration factor determined from observations in the tower of Westminster Cathedral. Further measurements at Westminster Cathedral showed that the vertical variation in gravity is not linear but is distorted near the base of the tower, probably due to local terrain effects.

Notes: Using the Cambridge pendulum apparatus the value of gravity at the National Physical Laboratory has been found to be 69.90 ± 0.16 mgal greater than that at the Ordnance Survey Office, Southampton. The result of a measurement with a Worden gravimeter was 70.36 mgal, and other indirect gravimeter measurements are in satisfactory agreement with the pendulum result.

Notes: Carbon dioxide and carbon monoxide: The rate of photo-dissociation of CO2 is appreciable only in the region above about 100 km. If local equilibrium prevails the carbon would occur mainly as the monoxide in this region, and as the dioxide below. However, oxidation may proceed so slowly that the life of a CO molecule is long compared with the characteristic time associated with atmospheric mixing effects. In this case the CO resulting from photo-dissociation would not be confined to above the 100 km level, but would extend much lower; its total abundance could scarcely be great enough to produce the observed absorption lines. It is estimated that the various forms of combustion taking place on the Earth would provide the CO content of the atmosphere within perhaps four years or even less. Methane: Dissociation of CH4 in the upper atmosphere is brought about mainly by collision processes. These prevent the existence of appreciable CH4 above the 100 km level and probably keep the concentration low even down to 70 km. The yield to date from oil wells and coal mines appears to be less than the amount of the gas now in the atmosphere. Seepage from fuel beds, and the anaerobic decay of vegetable matter, are the only obvious naturally occurring sources of significance. As far as can be judged at least ten years (and probably much longer) is required for the production of the atmospheric abundance. Nitrous oxide : Information on the necessary rate of formation of N2O is obtained by calculating the photo-dissociation rate. One hypothesis is that soil micro-organisms produce the gas, but it appears that the yield would only be sufficient if N2O were a major end-product of denitrification. Many of the homogeneous gas reactions suggested by earlier workers must be rejected, since there is an inadequate supply of the requisite parent particles. The only acceptable parent particles seem to be those arising directly or indirectly from the photo-dissociation of O2 in the Herzberg continuum. Various reactions involving O, O3 and N2 are discussed. Though they are very slow they might nevertheless give rise to sufficient N2O.

Notes: A definition of height is given in terms of the geopotential that will agree to the second order with the height determined by direct measurement along the vertical where such measurement is possible. The free-air reduction of gravity is carried to the second order so as to permit allowance for terms in eh and h2.

Notes: Times of P in Mediterranean, Japanese and Californian earthquakes are analysed with the objects of testing the generality of the increase of the velocity at short distances found in Europe and the evidence for Gutenberg's layer of low velocity. The Mediterranean earthquakes do confirm the increase at short distances, but the Japanese ones agree with the tables in use, and there is clear evidence of a regional difference. The evidence from North American earthquakes is conflicting. It does not definitely indicate any change from the present travel times, but the uncertainties are larger than in the other regions, chiefly because there are rarely enough stations in approximately the same azimuth and at greatly different distances to give much information.The difference of the times at 2° and 25° is about the same in Europe and Japan, but in comparison with them the times in Europe at 8° are about 3° earlier. The time-curve in Europe is nearly liner up to 14°. There is evidence in both regions for a strong curvature of the time-curve between 15° and 20°, but it does not decide whether dt/dΔ is continuous or discontinuous in this interval.The curvature of the time-curve is in any case surprisingly small, because laboratory studies of the variation of elastic moduli with pressure indicate an increase of velocity with depth several times that given by any set of travel times. Increase of temperature with depth would presumably reduce the rate of increase but does not appear sufficient to account for the discrepancy.

Notes: Tidal observations have been performed in the I. C. I. Salt Mine at Winsford. The gravimetric factor has been determined both for the overall values and the principal harmonic constituents. Its value is G= 1.20 ± 0.04. The results are compared with former measurements.

Notes: The analysis of a large number of observations of North Sea surges by R. H. Corkan has enabled him to make a classification of them into types. One type of surge appears to be due to the passage of an atmospheric depression over the entrance to the North Sea. By simplifying the mathematical conditions it is possible to predict the results of the passage of such a depression. These are largely in conformity with the observations. In particular it is shown that the surge produced is a progressive one, passing from the entrance to the North Sea to the closed end and increasing uniformly in amplitude.

Notes: On the basis of the study of the consolidation of clays made by Skempton (1944) and others, estimates have been made of the gravitational attraction of a deposit of clay. Examples of the behaviour of some typical clays are given and a procedure for correcting gravity anomalies for the attraction of a deposit of clay is suggested.

Notes: When a hot gravitating sphere cools, gravitational potential energy is lost in contraction. We consider a sphere that can be taken as in continual hydrostatic equilibrium for slow changes of state, and, assuming radial symmetry, set up the modified Fourier equation for heat conduction. This contains two extra terms, one contributed by the heating effect of contraction, and another from the change of temperature gradients with shrinkage. This equation is checked by integration through time and through the sphere to give a comprehensive energy equation.For an initial parabolic temperature distribution in the Earth, the heating effect of contraction is small, and more than counteracted by the extra cooling provided by increased temperature gradients. Moreover, it is probable that the modifications to the first (uniform rigid sphere) approximation which are needed to allow for departures from uniformity in density, specific heat, and thermal conductivity in the Earth are greater than those which allow for contraction.

Notes: A knowledge of the densities of rock formations is important in the interpretation of gravity anomalies. This paper describes the results of field and laboratory experiments made on the rocks in the Midlands of England. Density measurements were made on nine geological formations from the Silurian to the Cretaceous and also on Metamorphic rocks from the Malvern area. A catalogue of densities has been prepared for general use based on the assumption that rocks in the field are saturated with water. A table of densities and porosities for a large number of rocks is also given. Among the conclusions drawn about the observed sampling variances, the most significant is that rock formations in the West Midlands do not appear to show any” regional variation” of density. The results of the field and laboratory methods are consistent within the experimental errors of each, in marked contrast to the results reported by S. Hammer from observations in some American mines, from somewhat different data.

Notes: A critical examination is made of curves presented by W. M. Elsasser on the density and compressibility of materials at zero temperatures and pressures up to 30 million atmospheres, and of Elsasser's inference that the Earth's core consists of iron or nickel-iron. An argument leading Elsasser to suggest that the writer's Earth Models A and B may require adjustments because of discrepancies with Elsasser's results is shown to be invalid.New tables are presented which fit the data used by Elsasser at 30 million atmospheres and are also consistent with geophysical data. The calculations leading to these tables imply that the atomic number to be associated with the material of the outer central core should be at least six units less than the value derived using simple extrapolations from quantummechanical calculations for high pressures. If the reduction in the atomic number is no more than six units, the most probable composition of the material in question would still be nickel-iron, and to this extent Elsasser's main conclusion is supported. But there are other aspects of the new calculations which suggest that the needed reduction may be greater than six units; these aspects raise the probability that the outer central core consists of a modification of ultra-basic rock. A caution is issued against forming too definite conclusions on either of the two opposing theories on the whole evidence so far available.Some support is found for the view that the Earth's present inner core is more likely to consist of an accumulation of iron and denser materials than of ultra-basic rock that has undergone a second pressure transformation. Support is also found for the view that the density gradients of Model B require a progressive change of composition with increase of depth in the inner core. The hypothesis that the inner core is solid is strengthened. Strong support is given to Elsasser's argument against the presence of large amounts of compressed hydrogen in the central core.The new tables suggest that the density of uranium (Z=92) may be a fairly smooth function of pressure from zero pressure right through to 30 million atmospheres, but that, for elements of smaller atomic numbers, there are likely to be significant density jumps at specific intermediate pressures. Tables are presented which give newly computed densities of uranium from 0.1 to 30 million atmospheres, and may serve as a useful basis of discussion in other contexts.As an incidental to discussing Elsasser's arguments, an Earth model (Model X) has been constructed with the property that the density in the central core near its outer boundary is 6.5 g/cm3. The model has a density gradient in the mantle only a little steeper than that in Models A and B, and has somewhat greater densities in the inner core. The outer part of the central core (between depths of 2900 and 4980km), however, differs radically from that of Models A and B through having a far steeper density gradient. The new model has to be regarded as implausible inasmuch as the last property implies far greater changes of composition with depth in the fluid part of the core than anywhere in the mantle.

Notes: The theory of thermal instability in a sphere is extended to the case of a viscous sphere with a fluid core, the radius of the core being half that of the outer surface. The easiest mode to excite no longer corresponds to a spherical harmonic of degree I in the temperature but probably to degree 3 or 4. A more satisfactory model from the petrological point of view is based on the idea of a magma percolating through a mass of incompletely consolidated crystals. Results are obtained for this case, both for a uniform sphere and for one with a core. The harmonics of degree I are not the easiest to excite in either case. From analogy with other hydrodynamical problems it does not appear that these results offer any objection to the theory of the origin of the land and water hemispheres by thermal instability. The essential point is that, given sufficient time, the most widespread disturbances will become dominant provided only that they can be excited at all, and this condition is satisfied in all cases.

Notes: Two field gravity meters were read continuously for a period of 14 days, one at Peebles in South Scotland, the other at Kirklington near Nottingham. The experiments have shown that the observed variations of gravity were proportional to the predicted tide-raising force to within a standard deviation of 1/50, milligal. The factors of proportionality are 1.02 for Kirklington, and 1.10 for Peebles. There were no significant phase differences on the average; the individual phase differences were rather irregular.

Notes: Simultaneous tidal gravity measurements at Peebles and Kirklington over a period of 14 days have been analysed harmonically. The diurnal terms K1 and O1 give a ratio of observed to theoretical amplitude of G= 1.1 without significant phase difference. The semi-diurnal terms show a phase lag of about 10° and G= 1.2 at Kirklington and G= 1.1 at Peebles. This difference is explained as due to regional influences of sea-tides. G= 1.10 to 1.15 is regarded as the most probable value resulting out of these observations. The influence of temperature and pressure is discussed and the existence of a 24-hour period of non-gravitational origin (“thermal tide”) confirmed. The most probable values of Love's numbers “k” and “h” and the geophysical consequences as to the properties of the interior of the Earth are discussed.

Notes: Reviews in this articles:Willlam P. D. Wightman: The growth of scientific ideas.IIIe Congrès National des Sciences organisé par la Fédération belge des Sociétés Scientifiques, Brurelles, 30 Mai—3 Juin 1950.Edmund Whittaker: A history of the theories of aether and electricity. Vol. I: The classical theories.Charles Singer: A history of biology. A general introduction to the study of living things.Emile Callot: La renaissance des sciences de la vie au XVIe siècle.Agnes Arber: The Natural Philosophy of Plant Form.Howard Reed: Fan Ingenhousz, plant physiologist. With a history of the discovery of photosynthesis.Martha Teach Gnudi and Jerome Pierce Webster: The Life and Times of Gaspare Tagliacozzi, Surgeon of Bologna, 1545–1599, with a Documented Study of the Scientific and Cultural Life of Bologna in the Sixteenth Century.Cyril Elgood: A Medical History of Persia and the Eastern Caliphate from the earliest times until the year A. D. 1932.R. J. Forbes: Metallurgy in Antiquity. A notebook for archaeologists and technologists. With 98 illustrations.