21 8 



NATURE 



[October 13, 192 1 



by one-sixth, and Prof. Joly's conclusion is that 

 in Caledonian times there existed a metope of the 

 uranium which we now know, with possibly very 

 different properties. If this is true, the uranium 

 clock has not been keeping uniform time, and the 

 true age of the earth cannot be found by pre- 

 suming that it has done so. 



Prof. Sollas proceeded to explain and criticise 

 the arguments whereby geologists are seeking to 

 modify estimates of age based upon sedimenta- 

 tion, sea salinity, and denudation, so as to bring 

 them more in accordance with radio-active and 

 other physical calculations. He evidently con- 

 sidered these modifications not only premature 

 (for reasons given earlier), but to some extent 

 unsound. Geologists, he said, are not an un- 

 divided family, and proceeded to dissent, in 

 anticipation, from the views of Prof. J. W. 

 Gregory, read afterwards in abstract, owing to 

 his regrettable absence, by Prof. Jehu. The 

 necessity for modification of the hundred million 

 years or so, based on the original salinity 

 argument, was stated by Prof. Gregory to 

 be due to certain omissions and untenable 

 assumptions. It was assumed that the sea 

 was originally fresh, although the oldest 

 fauna, the Cambrian, has marine characteristics, 

 and no allowance was made for large supplies of 

 sodium chloride raised by magmatic waters from 

 beneath the earth's surface. Denudation also 

 was supposed to be uniform, although it was 

 very improbable that this had begn the case. The 

 earth is now under the influence of a time of 

 quick movement, whereas formerly it had alter- 

 nated between times of repose and activity, owing 

 to deformations which it had undergone. (One 

 cannot refrain from quoting Prof. Sollas's com- 

 ment that "we must no longer picture a time 

 when the earth was ' young and wantoned in her 

 prime,' but must suppose that she has exchanged 

 the passive indolence of youth for the fiery activity 

 of old age.") Altogether Prof. Gregory con- 

 sidered that the best-known geological estimates 

 might safely be multiplied ten- or twenty-fold, thus 

 bringing them into line with the physical evidence. 



Prof. Eddington brought forward interesting 

 evidence based on astronomical observations. He 

 described the observed behaviour of certain vari- 

 able stars, of which S Cephei is a typical example, 

 in which there is strong reason for supposing that 

 the fluctuations of intensity are due to some in- 



trinsic property of the star, and not to external 

 influence. The observed change of period (itself 

 a few days) of 5 Cephei has been proved by a long 

 series of measurements to amount to 008 sec. per 

 annum, or i per cent, in 58,000 years. If the 

 periodicity is associated with "pulsation" of the 

 star it will be related also to the density in such 

 a manner that the density of the star is changing 

 at the rate of i per cent, in 29,000 years. From 

 considerations of the luminosity of the star — a 

 red "giant" — it would require an increase of 

 density at the rate of i per cent, in joriy years to 

 provide the necessary energy according to Lord 

 Kelvin's gravitational contraction hypothesis. 

 We may conclude (i) that the star certainly has 

 sources of energy other than gravitation, and 

 (2) that Lord Kelvin's time scale should be 

 lengthened in the proportion 29,000 : 40, or about 

 700: I, at least during this stage of its evolution. 

 A considerable factor of the same kind would be 

 required for the sun also, even though its evolu- 

 tion has progressed much further, so that it is 

 now a "dwarf" star. 



Owing to lack of time it was not possible 

 for Dr. H. Jeffreys to take a verbal part in the 

 discussion, and his remarks were communicated 

 afterwards. Dr. Jeffreys 's calculations are 

 based upon two distinct considerations : (i) the 

 temperature distribution downwards in the earth's 

 crust, taking into account the radio-active con- 

 tent ; and (2) the tidal theory of the origin of the 

 solar system. It is not possible to do them 

 justice here, but we propose to publish them in 

 a later issue. Both theories lead to the 

 estimate of approximately 2 x 10^ years since the 

 solidification of the earth's crust, which is in re- 

 markable agreement with the results of other 

 physical methods. 



Sir Oliver Lodge, in a few words at the end of 

 the discussion, pleaded for justice to Kelvin, 

 whose calculation specifically assumed that "no 

 source of energy other than gravitation existed." 

 But Dr. Dear, with a rare eloquence which de- 

 lighted the audience, would not let the matter 

 rest there, but asserted that Kelvin arrived at his 

 twenty-million-year estimate by three distinct 

 methods, and regarded it as unalterable. 



In closing the discussion the president. Prof. 

 O. W. Richardson, laid stress upon the necessity 

 for further careful experiments for the final 

 elucidation of the problem. 



The Constitution of Molecules. 



THE joint discussion on the "Constitution of 

 Molecules " by Sections A and B of the 

 British Association aroused great interest, and 

 the audience, which filled the large meeting room 

 to its utmost capacity, included many visitors from 

 other sections. Dr. Irving Langmuir introduced 

 the subject with a clear and attractive presentation 

 of the theory which is associated with his name and 

 With that of Prof. G. N. Lewis- As originally 

 published, this theory depended on a rather large 



NO. 271 1, VOL. 108] 



number of arbitrary assumptions, but it has since 

 been greatly simplified, and now involves only the 

 three postulates described in Nature of September 

 15, p. loi. The first of these postulates, accord- 

 ing to which the electrons arrange themselves in 

 the atom in definite layers of 2, 8, 8, 18, 18 and 

 32, is sometimes in conflict with the third, which 

 requires that the residual charge on each atom 

 and group of atoms should tend to become a 

 minimum, and by giving greater weight to 



