March i, 19 17] 



XATU'RE 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous comtnunications.\ 



British Optical Science. 



The following paragraph is taken from a report on 

 itional instruction in Technical Optics, published re- 

 ntly under the auspices of the Board of Scientific 

 cieties : — 



A further need, which is urgent, is the supply of 

 mdard text-books dealing with those parts of Optics 

 nich at present are greatly neglected in this country ; 

 this includes practically the whole of Geornetrical 

 Optics and a large part of Technical Optics. In our 

 opinion the quickest and most effective method of 

 dealing with this requirement is by publishing transla- 

 tions of existing foreign books and abstracts of im- 

 portant papers on the subject." 



The recommendation contained in the last part of 

 this extract is admirable if carefully carried out, and 

 applies to all substantial scientific literature, 

 as well as to Geometrical Optics. But the reason 

 assigned, though doubtless prompted only by our 

 national habit of self-depreciation, is unwittingly a 

 reflection on the numerous treatises on the subject, 

 some of them of high originality, and of Continental 

 repute to judge from the references to them, that exist 

 in the English language. If the reason advanced had 

 been that many of these treatises are weak on the 

 technical side, which is important, not on account of 

 scientific principle, but solelv or mainly through its 

 connection with workshop practice, it would have 

 struck the mark. It is in British optical manufacture, 

 not in British University instruction and discovery, 

 that there has been lack of appreciation,, until recent 

 years, of what organisation, and co-operation between 

 theory and practice, can do, and have done in other 

 countries. It is in the trade that we had fallen behind, 

 for the usual reason that it is easy and profitable to 

 hold an agency for an efficient and pushing foreign 

 organisation, but quite another matter to compete 

 with it. The works of Heath, Herman, C. S. 

 Hastings, Schuster, R. W. Wood, and many others 

 dealing with Geometrical Optics (not to mention the 

 encyclopaedia articles of Lord Rayleigh and other 

 writers) do not seem to be in any w^ay inferior to 

 Continental books, themselves not very numerous; as 

 regards the substantial number of recent works on 

 the technical side of the subject by English and 

 American writers I am not much in a position to 

 judge, for the reason indicated above, but I see no 

 ground to doubt their value. Nor, within my own 

 knowledge, is there any ignorance of the higher 

 development of Geometrical Optics in such a technical 

 school as the Northampton Institute at Clerkenwell. 



In fact, one may be pardoned for what otherwise 

 might seem an invidious remark, that in the vast 

 expansion of optical science and practice during the 

 last century this country has had more than its share. 

 The evolution of the spectroscope, the mightiest 

 modern weapon of astronomical and ultimate physical 

 research, has been effected mainly in England and 

 America : names such as Rayleigh, Rowland, and 

 Michelson at once occur to mirid. For a long period 

 the construction of the great telescopes of the world 

 was a British and Irish speciality; it has now gone 

 largely to .America because it is there that they are 

 wanted. One need only glance at the references in 

 Czapski's admirable book — itself an excerpt from a 



XO. 2470, VOL. 99] 



German Encyclopaedia of Physics — to see that the 

 treatment of aberrations was set on a scientific basis 

 mainly by J, Herschel and Airy and Coddington. The 

 early theoretical work of Roger Cotes and R. Smith 

 was indeed largely anticipated in Holland by Huygens; 

 but one can imagine what a gap would.be made in the 

 science if the Geometrical Optical work of Thomas 

 Young, Sir VV'. Rowan Hamilton, and others named 

 above, and more of comparable merit still happily in 

 active production, were excluded. 



On the other hand, there is the old Munich school of 

 Fraunhofer and Steinheil, with their theorist in aber- 

 rations, von Seidel, of supreme rank, though now a 

 thing of the past. But the great modern object-lesson 

 is the scientific organisation and commercial success of 

 the firm at Jena xinder the direction of Zeiss and 

 Abbe, apparent mainly in the smaller optical appli- 

 ances which are commercial articles. It has been 

 due, as is well known, largely to their enterprise in 

 making experimentally all the kinds of glass that had 

 a chance of proving useful, and tabulating their optical 

 qualities. But the very same problem was attacked 

 in this country more than half a century ago by a 

 solitary scientific worker — the Rev. W. Vernon Har- 

 court — and pursued for many years into practical re- 

 sults with the unrivalled advisory- collaboration of Sir 

 George Stokes ; and it is understood to be generally 

 admitted that, with the aid of even a very small 

 subsidy from public sources, their neglected labours 

 would have solved the problem that in other hands 

 has carried so much dclat. Nor should the public- 

 spirited work of British glass-makers be forgotten, in 

 our new-born and most praiseworthy zeal ; the improve- 

 ments effected at Chance's works at Birmingham 

 under the direction of John Hopkinson are classical, 

 and the inspiring energy^ of Sir David Gill promised 

 just before his death fruitful dA'elopments in the 

 astronomical direction, both there and at Black friars. 



Joseph Larmor. 



Cambridge, February 17. 



The Bursting of Bubbles. 



The interesting letter appearing under the above title 

 in the issue of Nature for February 15 reminds me of a 

 different, but equally simple, method of producing the 

 same phenomenon, described in the Proceedings of the 

 Physical Society, vol. xxviii., p. 59, 1915. There, in 

 order to avoid obscuring the issue, the bubbles are 

 said to discharge minute clouds of smoke ; but, as 

 often as not, smoke-rings like those described by Mr. 

 Campbell Swinton and Miss Beale were obtained by 

 Mr. Moss. In this method bubbles (of air) of any 

 desired size can be used. These are filled with smoke 

 by placing a wire, conveying a current of appropriate 

 strength (easily determined by trial), above the end of 

 the tube through which they enter the oil. A similar 

 phenomenon is exhibited, very effectively, in a well- 

 known experiment with phosphoretted hydrogen. 



S. W. J. Smith. 



Imperial College of Science and Technology, 

 February 16. 



Thermodynamics and Gravitation: A Suggestion. 



The recent experiments of Dr. P. E. Shaw {Phil. 

 Trans., ccxvi., 1916) seem to show that the "gravita- 

 tion constant " has a temperature coefficient. It is 

 remarkable, too, that G seems to be only appreciably 

 influenced by increasing the temperature of the larger 

 attracting mass. 



The application of the principles of thermodynamics, 

 while aflfording no explanation of gravitation itself, 

 may oflfer an explanation of the temperature coefficient 

 if it exists. One assumption only is required, namelv, 



