December 9, 1922] 



NA TURE 



77i 



Acoustic Research. 



The editorial article on the subject of " Acoustic 

 Research," in Nature of October 28, p. 565, conveys 

 an impression which seems to need correction. 



In justice to the life-long labours of the late Prof. 

 W. C. Sabine, now gathered into a volume of " Col- 

 lected Papers on Acoustics " (Harvard University 

 Press), it should be said that the practical problem of 

 predicting the acoustics of an ordinary auditorium in 

 advance of its construction, or of correcting one 

 already built, was solved by Prof. Sabine some twenty 

 years ago. The essential feature to be considered in 

 such a problem is the reverberation, and Sabine's 

 papers on this subject are full and complete. Other 

 acoustic questions are, of course, sometimes involved, 

 such as the transmission of sound through walls, the 

 effect of resonance, etc. Several of these had also 

 been the subject of prolonged experimental investiga- 

 tion by Prof. Sabine at the Jefferson Physical Labora- 

 tory at Harvard, but some of the results were withheld 

 until the work could be completed. His untimely 

 death interrupted this programme, and since then the 

 work has been continued here, and at the Acoustical 

 Laboratories, Illinois, under the direction of Dr. Paul 

 E. Sabine, as described in Mr. Munby's article in the 

 issue of Nature of October 28, p. 575. 



Architects in the United States have become aware 

 of the importance of Sabine's results, and scores of 

 cases could be cited in which the application of the 

 principles worked out by him has led to complete 

 success. The opinion that " the laws regulating the 

 production of a successful building for hearing and 

 speaking have yet to be worked out " implies a lack 

 of respect for Sabine's profoundly accurate and 

 thorough work, which I am sure no one will maintain 

 who has taken the trouble to acquaint himself with 

 the subject. Theodore Lyman. 



Harvard University, Cambridge, Mass., 

 November 14. 



[The intention of the article to which Prof. Lyman 

 refers was to promote increased attention to acoustic 

 research ; and we regret that a phrase in it should 

 be regarded by him as implying a lack of respect for the 

 pioneer work done by the late Prof. Sabine. While 

 readily admitting the value and completeness of 

 Prof. Sabine's papers, the continued useful activities 

 of his acoustic laboratory would seem to indicate 

 that in the general sense intended the expression 

 used in reference to the need for further investigation 

 was justified. It may be true that rules have been 

 worked out upon which a perfect acoustic building 

 can be constructed ; the practical problem presented 

 to the architect, however, often takes the form of the 

 provision of acoustic success with prescribed limita- 

 tion in the matter of design, and it is in this direction 

 that further knowledge is needed. — Editor, Nature.] 



Separation of the Isotopes of Zinc. 



Pure zinc has been subjected to distillation in a 

 high vacuum, and after three fractionations of the 

 distillate the latter shows a lower density than the 

 original zinc. The residue has been reduced by 

 evaporation to one-twentieth of the original volume 

 and shows an increased density. The method of 

 separation is similar in principle to that of Br0nsted 

 and Hevesy for mercury. 



Two sets of distillations have been carried out. 

 In the preliminary set, last winter, the distillations 

 of the distillate were carried out too rapidly and too 

 great a quantity was distilled. The results for the 

 distillate indicated no separation, whereas the 

 separation of the residue, which was effected under 

 better conditions, showed an increase in density. 



NO. 2771, VOL. I IO] 



Another set of distillations was therefore carried out 

 this summer under improved conditions (using liquid 

 air condensation and a more careful regulation of 

 the temperature and the quantity distilled). The 

 final distillate is lighter and the final residue heavier 

 than the original zinc. The determination of the 

 density of a metal, as ordinarily performed, is no 

 criterion of the average atomic mass per unit volume. 

 The main part of the work has therefore been directed 

 towards making it so ; the only alternative appears 

 to be the determination of the atomic weight to an 

 accuracy of about 1 part in 10,000. The presence 

 of flaws, of impurities, of allotropes, and of metal in 

 a different physical state do not sufficiently explain 

 the results ; the discussion of these four points will 

 be included in the publication of the work. 



Taking the density of the initial zinc as unity, the 

 density of the distillate is 0-99971, and of the residue 

 1-00026. These numbers appear to be outside the 

 error of 14 determinations of the density of 7 separate 

 samples of the initial material, for the greatest 

 divergence between the numbers obtained only 

 amounts to 0-00015. O n recasting the residue and 

 the distillate the difference is maintained. 



The separation indicated by these figures would 

 imply a change in atomic weight of about 3 J units 

 in the second place in the atomic weight. This is 

 considerably less than might have been expected if 

 the metal was composed of equal quantities of an 

 isotope of an atomic weight of 64 on one hand, and 

 of isotopes 66, 68, and 70 on the other hand. 



Alfred C. Egertox. 



The Clarendon Laboratory, Oxford, 

 November 21. 



A Curious Feature in the Hardness of Metals. 



By combining Meyer's formula 

 L — ad" 

 with that for the ordinary Brinell test 



ttD, 



H = L- -(D- V /D 2 -^) 

 the following relationship is obtained : 



H % i., ! .L^{D + ^-®"}. 

 In this the second term ceases to have a real 

 meaning when 



■>-©'■ 



Beyond the load corresponding to a value 



L=aD" 

 the hardness becomes imaginarv, or, in other words, 

 the load will be sufficient to force the ball through 

 the material continuously. This fact may well be 

 of considerable importance in connexion with such 

 questions as the penetration of a plate by a projectile, 

 in punching operations, and even in lathe work. 



In the case of a steel of 0-2 per cent, carbon and 

 o-6 per cent, manganese with a Brinell hardness 

 number of 140, using a ball of 10 mm. diameter, and 

 a load of 3000 kilograms, the values of a and n will 

 be about 74 and 2-29 respectively. Under these con- 

 ■ ditions the load at which perforation of the steel will 

 occur will be 14,400 kilograms, when the hardness will 

 have fallen to 92. 



Further work in this direction is being carried out 

 by one of us ; but the fact that there is a high load at 

 which the ordinary hardness measurements cease to 

 apply, and the possible significance of the fact, seemed 

 sufficiently interesting to warrant early publication. 

 Hugh O'Neill. 

 F. C. Thompson. 



The Victoria University of Manchester, 

 November 15. 



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