876 



NA TURE 



[December 30, 1922 



could concentrate on this subject, they would do 

 industry a real service, for nearly all industrial opera- 

 tions such as punching, shearing, forging, milling, 

 spinning, and, of course, the turning of metals, are 

 plastic flow phenomena. 



During experiments I carried out with heavy lathes 

 in 1908 for the purpose of finding the most economical 

 high-speed steel to use, I encountered some chips 

 which were not only straight but actually presented 

 concavity to the tool face, and I have one of these 

 chips now. They were produced at very high speed 

 on steel, and are mentioned in the discussion of a 

 paper read before the Siemens' Stafford Engineering 

 Society in 1908 (Proa, vol. 1, p. 93), on " The Plastic 

 Deformation of Solids." 



Brewster's beautiful photo - elastic method and 

 Professor Coker's important applications of it en- 

 able the stresses during elastic strain of the tool and 

 material in the region A to be computed, but Taylor, 

 in the work cited, has shown how a tool should be 

 forged and supported on the saddle to give it maxi- 

 mum life and maximum strength. 



Unfortunately for engineering industry in this 

 country, nearly all lathes are built with the vertical 

 space between the upper surface of the tool rest and 

 the line of centres far too small to enable Taylor's 

 important conclusions to be put into practice. 



Alan Pollard. 



Imperial College of Science and Technology, 

 November 29. 



I gather from Air. H. S. Rowell's letter published 

 in Nature for December 9 that, while interested in 

 the subject of the flow of metals in shavings, he is not 

 altogether familiar with the work that has already 

 been done on the subject. In a comprehensive 

 " Memoire sur le rabotage des metaux " (which can- 

 not be so well known as I have hitherto believed) 

 published more than forty years ago, M. H. Tresca 

 investigated the question of the curling of shavings, 

 both experimentally and mathematically, the actual 

 flow of the metal (expressed by a coefficient de 

 riduction) being especially selected for study under 

 very varied conditions. The following quotation 

 indicates only part of the scope of the work : " Ces 

 phenomenes sont aussi ceux dans lesquels, pour la 

 premiere fois, les metaux les plus durs, tels que 

 l'acier, le fer, se comportent en realite comme le 

 plomb, comme le savon, comme le cire, nous dirions 

 presque comme les liquides, tant est complet le 

 rapprochement que Ton doit faire entre les rides de 

 nos differents copeaux et de veritables vagues de 

 metal." 



The memoir is published as one of the " Memoires 

 presentes par divers savants a l'Academie des 

 Sciences de ITnstitut de France," tome xxvii., 1883. 

 Those familiar already with the beauty of the results 

 obtained will pardon this effort to direct the atten- 

 tion of others to the work. 



E. N. da C. Andrade. 



Artillery College, Woolwich, 

 December 11. 



The Secondary Spectrum of Hydrogen. 



Since the negatively charged hydrogen atom is 

 known to exist, from work on positive ravs, it seemed 

 likely that Silberstein's particular solution of the 

 three-body problem, applied by him to the case of 

 neutral helium (Astrophys. Jour., September 1922) 

 should also be applicable in this case. Consequently 

 the formula used by him was modified so as to apply 

 to hydrogen (charge E instead of 2E, and hence N 

 instead of 4N), and also a small but important correc- 



NO. 2774, VOL. I IOJ 



tion was made to the value of N so as to take account 

 of the fact that with two electrons instead of one, 

 the correction to the mass of the electron for the 

 finite mass of the nucleus is no longer the same. 



It was assumed as a first approximation that the 

 electrons would be arranged antipodally, and conse- 

 quently the forces would be again central. So 

 Curtis's value of N for hydrogen was corrected so 

 as to apply to a nucleus of infinite mass : 



»--*.(i + 5). 



Frequencies were then calculated from the formula 



= N„ 





These frequencies were then sought for in the 

 secondary spectrum of hydrogen ; it is known that 

 negatively charged atoms are to be found in hydrogen 

 at fairly high pressures with intensity quite com- 

 parable with that of the positively charged atom 

 (" Rays of Positive Electricity," p. 39). As a result 

 it was found that 47 lines in the secondary spectrum 

 agreed with the calculated values within an absolute 

 error of one unit of frequency, taking integral values 

 of n 2 and m 1 from 1 up to 10, and values of m 2 from 

 1 to 15, while »j was taken as 2 and 3. 



This means that the frequencies can be looked on 

 as a kind of " summation tone," being the sums of a 

 Balmer or a Paschen frequency and a frequency in 

 the infra-red. 



It was also found that in several cases a physical 

 similarity of behaviour was common to " series " 

 of the lines grouped according to the m's and n's 

 concerned, though this was not exclusively true. 

 As a standard of reference for the observed frequencies 

 the values obtained by Merton and Barratt (Phi). 

 Trans. A, 1922, pp. 388-400) were employed. 



As typical may be given the following : — 



Formula. Calculated. 

 16934-9 



Observer!. Error dv. 



17192-14 +0-16 0++CD++HP + He 



3++CD + HP ++He 



ho-66 o + He 



In the foregoing table, the figures in the last 

 column refer to intensity and the symbols to the 

 physical properties of the lines as given by Merton 

 and Barratt (loc. cit.). 



It is hoped to complete these and similar calcula- 

 tions shortly and also to investigate the conditions 

 under which these lines should be enhanced. 



A. C. Menzies. 



Physics Laboratory, The University, Leeds, 

 December 8. 



Science and the Empire. 



The admirable sentiments expressed in the leading 

 article in Nature of December 16 will undoubtedly 

 be re-echoed by every scientific worker in the country. 

 In stating, however, that the British Science Guild is 

 the only organisation which exists to undertake the 

 propaganda work " for the extension of an under- 

 standing of the influence of scientific research and its 

 results," the very effective propaganda which is being 

 carried out bv scientific workers themselves under the 



