78o 



NATURE 



[June 17, 1922 



(2) The figures [diagrams] show clearly that the 

 all-important fact has been missed, namely, that the 

 so-called aftershaft or byfeather consists not only of 

 a few simple barbs but also of a distinct shaft. 



(3) Perhaps it will save matters if we read : Some 

 owls and some petrels have as thick and fluffy and 

 long-lasting mesoptile coats as some penguins, re- 

 lativel}'^ of course. For example, if some nestling 

 feathers of the shearwater measure 24 +26 =50 mm. 

 in length, this does not prevent large penguins from 

 wearing still longer and longer-lasting coats ; nor is 

 it incompatible with some small petrels having mes- 

 optiles (they vary much according to position) less 

 than half an inch in length. 



Perhaps some genius, not too much hampered by 

 facts, may still discover a " law," or equation by 

 which the palaeontological dates of various groups of 

 birds can be deduced from the relative emanations 

 of their successive nestling coats. H. F. G. 



The Atomic Weight of Mercury from 

 Different Sources. 



The successful accomplishment of separating the 

 isotopes of mercury (Nature, 106, 144, 1920 ; Phil. 

 Mag. 43, 31, 1922) suggested an investigation to 

 determine the extent to which samples of mercury 

 from different sources might show the same atomic 

 weight, i.e. the same density, which is to be expected 

 only if the various minerals contain the isotopes in 

 the same ratio. 



Mercury obtained from the following minerals was 

 investigated : — 



Mineral. Geological Period. 



1. Cinnabar from Almaden (Spain) Silurian. 



2. ,, ,, Phalz (Germany) Permian. 



3. ,, ,, Idria (Dalmatia) Triassic. 



4. ,, ,, California (U.S.A.) Cretaceous. 



5. ,, ,, Santafiora (Italy) Eocene. 



6. ,, ,, Ras-el-Mah (Tunis) Upper Eocene. 



7. ,, ,, Golnicz (Hungary) 



8. Calomel ,, Terlingua (U.S.A.) Lower Cretaceous. 



9. Mercury oxychloride, Terlingua 



(U.S.A.) Lower Cretaceous. 



10. Cinnabar, synthetic, unknown origin 



After reduction with iron and repeated distillation 

 of the metal in vactw the densities were measured 

 by the method described in the previous communica- 

 tion. We found no difference in density exceeding 

 the possible experimental error, which amounted to 

 2-6 in a million, corresponding to o-ooo4-o-ooi2 

 in the atomic weight. Considering the very different 

 geological and geographical origin of the mercury 

 samples investigated we can conclude, with great 

 probability, that the isotopic composition of mercury 

 of terrestrial origin is the same. 



The following numbers are the density data (i/) 

 found in the literature : — 



13-5959 (Regnault, 1807). 

 13-5958 (G. de Metz, 1892). 

 13-5956 (Vincenti and Omodei, 1888). 

 13-5953 (Volkmann, 1881). 

 13-5938 (Marek, 1883). 

 13-5937 (Thiesen and Scheel, 1898). 

 13-5886 (Biot and Arago, 1816). 

 The considerable differences exhibited by several 

 of these numbers do not exclude the possibility that 

 mixtures of different isotopic composition were 

 measured. From the above-mentioned investiga- 

 tion, however, we are justified in assuming the 

 differences as most likely due to experimental errors. 



J. N. Bronsted. 

 G. Hevesy. 

 Physico-Chemical Laboratory of the Polytechnic 

 High School, Copenhagen, May 12, 1922. 



NO. 2746, VOL. 109] 



The English Ph.D. 



Some time ago I had the privilege of listening to 

 addresses by the heads of two prominent English 

 colleges on the provisions for the English Ph.D. 

 Quite frankly it was stated that this degree is intended 

 to satisfy students from the Dominions and the 

 United States. It is manifestly unfair to give an 

 American, for example, as a result of his study a 

 degree, like M.A., which is of little or no value in 

 his own land. 



Two fundamental mistakes, however, have been 

 made which endanger the value of the English Ph.D. 

 Perhaps this can be made clear by considering the 

 matter from a purely practical aspect. The American 

 undergoes the expense of his work for the Ph.D. 

 primarily because it helps him to a better post than 

 he would otherwise get. If his degree does not 

 help him to earn his living it has no more than a 

 sentimental value. When applying for his post, his 

 degree is weighed by the faculty and other authorities. 

 It is their opinion that determines the character of 

 the university work for the Ph.D. 



These people require evidence that the candidate 

 has received what they consider to be the best train- 

 ing. In the first place, his degree must be from a 

 place where his subject is well taught. For a post 

 in geology the degree from a university where geology 

 is represented by a distinguished professor is a valid 

 claim, whereas one from a university with a less 

 able geologist is of lower value. The English uni- 

 versities must recognise that the value of their 

 Ph.D. depends on the distinction of their teachers 

 and not on their antiquity or fame. 



The general intellectual training of the man is 

 a second factor. His degree must mean that he is 

 imbued by the spirit of scientific research derived 

 through contact with the leading ' investigators. 

 This implies immediately that for the particular 

 departments which the university decides to develop 

 the Ph.D. instruction, it must have professors of the 

 first rank.' A general all-round training, at least 

 in the man's particular subject, is also demanded. 

 This implies that the student must spend his time 

 at different universities. The man who has worked 

 in physiology under Sherrington, Bayliss, Starling, 

 and Langley is a better-trained man than one who 

 has spent his whole three years with only one of 

 them. The English system, however, seems to deny 

 or discourage the principle of migration. Unless 

 something like the German system of free migration 

 is developed the English degree can never have a 

 value equal to the old German one. 



It is not necessary to discuss certain other regula- 

 tions ; they will lapse by their own failure. For 

 example, one university has proposed that the 

 student shall choose his problem of investigation 

 at the beginning of his three years and devote himself 

 mainly to following it under the guidance of the 

 professor. Such a process would turn out a narrow- 

 minded monk, and not the all-sided man of science of 

 wide views that is demanded. Most of the regula- 

 tions proposed by the universities are aimed at keep- 

 ing out unfitted students — quite proper but minor 

 considerations. In none of the discussions that I 

 have heard has there been any conception of the 

 more important matter of providing for the proper 

 development of the scientific investigator with the 

 gift of presenting his results to the world. Yet this 

 is just what the American universities demand from 

 candidates for vacant posts. What these provisions 

 must be I will not attempt to indicate. They can 

 be discovered only by careful inquiry into the causes 

 of the success of some universities and the stagnation 

 of others. E. W. Scripture. 



