March io, 192 i] 



NATURE 



43 



that ^ remains unchanged. His second result [Phil. 

 Mag., vol, xxxvii., p. 149) shows that a remains un- 

 changed. The time of the double journey is accord- 

 ingly obtained by replacing u by u+v in expression (2), 

 and the Michelson-Morley result requires that equa- 

 tion (3) shall remain true when u+v replaces u. Since 

 Majorana's results held over a considerable range of 

 values of v, it appears that (3) must be true for a 

 whole range of values of u, requiring at once 

 a = /3 = o, so that the two terms in expression (i) 

 must represent separately the times of the inward 

 and outward journeys. 



Translate this into relativity language, and it 

 appears that when x, t, x\ t' are related by the 

 usual Lorentz transformation, then the Michelson- 

 Morley experiment, when supplemented by the ob- 

 servations of Majorana, shows that both on the out- 

 ward and on the inward journey light travels with the 

 same constant velocity c. J- H. Jeans. 



Relativity and the Deviation of Spectral Lines. 



The prediction of the Einstein spectral-line effect 

 rests on two assumptions, namely, (i) the radiating 

 source behaves as a natural clock, and {2) the time- 

 period of the source is transmitted by the radiation 

 to the observer. 



An alternative to the second of these assumptions is 

 that the radiation transmits the Einstein interval ds 

 rather than the time interval dt of a vibration. This 

 alternative appears to be more in accordance with 

 the general ideas of relativity. 



Consider two light pulses leaving A at times 

 ^A, tx+dix, and arriving at B at ^b, t^ + dtn. Since 

 ds=o along the w-orld line of each pulse, it appears 

 that the interval y^dt,^ between the two departures 

 from A is equal to the interval y^dtn between the 

 arrivals at B — that is, the Einstein interval, and not 

 the time interval, is transmitted. 



If this contention be correct, the Einstein effect 

 should arise, not from the transference of the source, 

 but from the transference of the observer to a different 

 gravitational field. 



It may be contended that the use of the principle 

 of least time in the ordinary method of deducing the 

 deviation of a beam by a gravitational field pre- 

 supposes an underlying constant time period in the 

 radiation. To this I would reply that it is possible 

 to deduce the deviation without any reference to pre- 

 Einstein physics. I propose to deal with this point 

 in a communication to the Philosophical Magazine. 



H. J. Priestley. 



University of Queensland, Brisbane, 

 January 15. 



Amplifying the Optophone. 



Mr. Campbell Swinton's forecast in Nature of 

 March 3, p. 8, has been fully verified since he wrote. 

 On Tuesday, March i, the Marconi Co. kindly lent 

 me one of their three-valve amplifiers working with 

 an S. G. Brown loud-speaking telephone and wooden 

 trumpet. Mr. F. Swann, of the Marconi Co., per- 

 sonally superintended the installation, and we suc- 

 ceeded without much difficulty in producing a sound 

 which made ordinary printed matter "legible" to 

 several blind pupils in a room. A reading demonstra- 

 tion from the amplified sound was given in the 

 presence of Sir William Collins and Mr. C. P. 

 MacCarthy. 



This new development marks a great step forward, 

 and I consider that Mr. MacCarthy and Mr. Camp- 

 bell Swinton deserve credit for their initiative In this 

 matter. E. E. Fournier d'Albe. 



10 St. James's Terrace, N.W.8, March 5. 

 NO. 2680, VOL. 107] 



With reference to the letter on the above subject 

 in Nature of March 3, it may be of interest to record 

 that thermionic amplifiers were applied to the opto- 

 phone a considerable time ago with the object of 

 increasing the sound in the ordinary telephone, but 

 although it was evident that the sound could be 

 amplified, it was decided that to increase the cost and 

 complexity of the instrument to the extent Involved by 

 the addition of an amplifying set was not justified. 



In 1919 Messrs. Barr and Stroud, Ltd., applied to 

 Messrs. Marconi, of Chelmsford, who were kind 

 enough to prepare a special amplifying set. 



At a later date, through the kindness of Major 

 Henrici, the valuable advice and assistance of officers 

 of the Signal Department at Woolwich were also 

 obtained. 



Mr. Swinton, by the application to the subject of 

 his great experience of amplifiers, has attained most 

 encouraging results In making the optophone notes 

 audible for instructional purposes. 



James Weir French, 

 Director, Barr and Stroud, Ltd. 



Anniesland, Glasgow, March 7. 



The Peltier Effect and Low-temperature Research. 



I WAS much interested to see Mr. A. A. Campbell 

 Swinton's letter to Nature of February 24, p. 828, 

 on the above subject. So far as I am aware, the 

 first suggestion to attain low temperatures by means 

 of the Peltier effect was made by me when 

 a student some twenty years ago. If Mr. 

 Campbell Swinton will look up Nature of August 15, 

 1901, p. 376, and also the Chemical News, 1901, 

 vol. Ixxxiv., p. 73, he will see an article by 

 myself entitled "On a Possible Method of Obtaining 

 the Absolute Zero of Temperature," in which the 

 method is suggested in detail. There is little doubt 

 that a great field of research would open out once the 

 absolute zero of temperature were obtained, and tem- 

 perature as a phase vanished from matter. 



Attention may also be directed to a paper by Mr. 

 Brinkworth and myself entitled " On the Heatless 

 Condition of Matter " in Chemical News, 1902, vol. 

 Ixxxv., p. 194. Of course, it must be recollected that 

 we were writing twenty years ago, long before modern 

 developments occurred. Unfortunately, I have been 

 out of touch with such matters, and have not had the 

 opportunity of seeing whether any researches have 

 been carried out on these lines owing to my work 

 developing in a different direction. 



Geoffrey Martin. 



109 Corporation Street, Manchester, 

 March 2. 



With reference to Dr. Geoffrey Martin's interesting 

 letter, It was because I thought it very possible that 

 the idea was not new that I put my suggestion In the 

 form of an Inquiry. I have looked up his several 

 most suggestive papers, which fully bear out what 

 he says. 



As I have pointed out, since the date of Dr. 

 Martin's communications to Nature and to the 

 Chemical News in 1901, Prof. Kamerlingh Onnes has 

 verified the disappearance of electrical resistance at 

 very low temperatures which Dr. Martin, amongst 

 others, predicted. It does not appear certain whether 

 at such temperatures, when electrical conductivity in 

 metals becomes infinite, either the Peltier effect or 

 the corresponding opposite thermopile effect would 

 operate. 



Perhaps these effects may be enhanced, but possibly 

 they may disappear; much would appear to depend 

 upon how these low temperatures affect heat conduc- 



