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NATURE 



[January 26, 1922 



Tribal Name of the Raninidse. 



In the report of the Linnean Society's meeting on 

 December 15 last the abstract of an elaborate and 

 highly important essay by Prof. G. C. Bourne on 

 "The Raninidae : A Study in Carcinology " contains 

 a proposal to place the family "in a separate tribe, 

 Gymnopleura. " 



It would seem, however, that the name for such a 

 tribe has been anticipated by Latreille, who, under 

 date 1831, in his "Cours d'Entomologie, " p. 368, 

 institutes the tribe Notopterygia expressly for .the 

 genus Ranina. Attention has been directed to this in 

 the comparatively recent year 1908 in the Annals 

 of the South African Museum, vol, 6, p. 17. The 

 same page explains that the specific name in Ranina 

 dentata is founded on a mistake, and the preceding 

 page, while giving a wrong date to the Mantissa of 

 Fabricius, will by its synonymy justify the substitu- 

 tion of Ranina raninus, Linn., in preference alike to 

 R. scabra and R. dentata. 



Thomas R. R. Stebbing. 



Tunbridge Wells, December 22. 



I AM far from a scientific library and unable to 

 verify Mr. Stel?bing's reference to Latreille 's classifica- 

 tion of the Rariinidse, but have not the least doubt 

 that the referencie is correct. There is no reference 

 to Latreille 's tribe Notopterygia either in Milne 

 Edward's " Histoire Naturelle des Crustac^s " or in 

 de Haan's "Crustacea" in Siebold's "Fauna 

 Japonica," and as I was concerned rather with the 

 correction of existing schemes of classification than 

 with the work of earlier authors, Latreille 's "Cours 

 d'Entomologie " escaped my attention. Had I read 

 it I should have suggested the restoration of Latreille 's 

 tribe, giving to it the new definition set forth in my 

 memoir communicated to the Linnean Society, and 

 it seems that my proper course will be to withdraw 

 the name " Gymnopleura " and substitute that of 

 "Notopterygia, Latreille," in an addendum to the 

 printed paper. G. C. Bourne. 



Twyning Manor, Tewkesbury, December 30. 



The Depth of Earthquake Focus. 



In the Philosophical Transactions of the Royal 

 Society, Series A, vol. 222, pp. 45-56 (192 1), Mr. G. W. 

 Walker, relying on certain observations of the 

 emergence-angle of P waves at Pulkovo, makes the 

 somewhat startling suggestion that the depth of focus 

 is of the order one-fifth of the earth's radius, or about 

 1250 km. This is a much larger estimate of depth 

 than that hitherto ■ suggested, viz. of order less 

 than 100 km. Mr. Walker's estimate of depth is a 

 consequence of accepting the Pulkovo numbers as 

 correct. It appears that the values of the apparent 

 angle of emergence calculated from Zoppritz's curve 

 do not agree with its value directly measured at Pul- 

 kovo. This discrepancy is so marked that either the 

 time-curve or the Pulkovo. values must be seriously in 

 error, and Mr. Walker proceeds on the assumption 

 that within the limits of possible error in the time- 

 curve we can modify it so as to agree with the direct 

 measure of the apparent angle of emergence. 



It appeared to me that in a matter so important 

 independent proofs would be desirable, and an attempt 

 has been made to obtain an estimate of depth from 

 the following considerations :— For a very deep focus, 

 the long-wave phase in the seismogram or the "main 

 strock '' identified with the arrival of Ravleigh's two- 

 dimensional surface-waves would be of diminished 

 importance compared to the P and S phases which 

 are due to the three-dimensional longitudinal and 

 transverse waves travelling by brachistochronic paths 

 from focus to station, in view of the fact that the 

 NO. 2726, VOL. 109] 



surface-waves are originated by the shocks in the 

 epicentral region. These shocks in their turn are due 

 to the arrival of the longitudinal and transverse waves 

 from focus to the epicentral region, and these waves, 

 Varying as they do as the inverse powers of the dis- 

 tance, make the shock in that region of lesser and 

 lesser intensity the greater the depth of the focus. 

 Consequently, the depth to be chosen for the focus 

 must be of such a magnitude that the observed rela- 

 tionship between the principal phases in the seismo- 

 gram is maintained. It has been found possible to 

 calculate the effects of various focal depths on the rela- 

 tive importance of the different phases in the seismo- 

 gram by an extension of the procedure adopted by 

 Lamb in determining the propagation of tremors on 

 the surface of an elastic solid (Phil. Trans., A, 

 vol. 203, 1904). The investigation suggests that the 

 hitherto accepted estimate of depth of focus is much 

 nearer the truth than Mr. Walker's estimate. The 

 detailed calculations will be pubUshed in due course. 



S. K. Banerji. 

 University College of Science, Calcutta, 

 December 22. 



Energy Changes Involved in Transmutation. 



In some recent discussions concerning the possibility 

 of the transmutability of large amounts of one element 

 into others— and particularly that of lead into gold — 

 no mention has been made .of the energy changes 

 involved. Studies in radio-activity and the work of 

 Sir Ernest Rutherford have shown that whenever an 

 element breaks up a relatively enormous quantity of 

 energy is liberated. 



Should it ever become possible to control the break- 

 ing up of elements, the advantages to be gained will 

 lie in two main directions. First, the manufacture 

 of elements now scarce from those more plentiful will 

 be of the utmost value to industry. Secondly, the 

 fact that intra-atomic energy will then be available 

 should provide a satisfactory solution to the problems 

 raised by the world's dwindling sources of power. 



But if the energy available in this way is ever 

 extensively used, all the heavier elements will be 

 destroyed and gradually replaced by lighter ; at the 

 same time their available energy will be lost. So it 

 appears possible that after countless ages the earth 

 may become a mass of light elements, possibly in 

 the condition of a nebula. 



It has been assumed above that it would be possible 

 to control the decomposition of elements so that only 

 a limited amount of energy was liberated at a time. It 

 is of some interest to contemplate what will happen 

 should this evolution of energy get out of hand. 



Let us suppose that someone has succeeded in 

 starting the rapid decomposition of a block of a heavy 

 element by the use of some accelerating influence. If 

 the energy liberated during the action can escape 

 faster than it is set free, no violent action is to be 

 expected ; but if, on the other hand, it is liberated 

 faster than it can escape, an action of explosive 

 violence may occur. The accumulation of energv will 

 certainlv increase the rate of decomposition of sur- 

 rounding atoms, which in their turn will add still 

 more energy, and the change will go on with ever- 

 increasing velocity until the whole block of the element 

 is destroyed. Should the surrounding elements be un- 

 able to stand up against the enormous quantity of 

 free energy at their surfaces, it seems that nothing 

 could save the earth from complete destruction. Thus 

 inadvertently the world might be reduced by some 

 enterprising chemist or physicist (o a white-hot 

 nebulous mass. I. W. Wark. 



43 Vincent Square, S.W.i. 



