NA TURE 



[September 29, 1904 



In this connection it should be observed that it is a general 

 rule that when a molecule adds on atoms to itself, the 

 resultant aggregate of atoms usually exerts an intensity of 

 molecular attraction less than that of the original molecule. 

 For example, high-grade types of combination are nearly 

 always more volatile than lower types of combination of 

 the same molecular weight. Saturated compounds are more 

 volatile than unsaturated compounds of the same molecular 

 weight. Chemically unstable compounds are invariably 

 more volatile than stable compounds of the same molecular 

 weight, and the addition of atoms to a molecule decreases 

 its stability. 



The point is discussed fully in a paper which appeared 

 in the Chemical Neuis some time ago (vol. Ixxxix. p. 241). 



We should therefore expect to find that when a substance 

 A in a liquid combines with molecules of the liquid, the 

 intensity of the molecular attraction which the new com- 

 pound exerts would diminish as the number of molecules 

 of the liquid added on to the molecule A increases. 



When this is not the case, van 't Hoff's law cannot be 

 obeyed at all closely by the dissolved substance. 



Kiel, September 6. Geoffrey Martin. 



THE ROYAL PHOTOGRAPHIC SOCIETY"; 



ANNUAL EXHIBITION. 

 'X*HIS e.xhibition will remain open until October 

 -•• _ 2g._ Althoug^h the scientific and technical 

 section is disappointing, for, taken as a whole, it 

 is below the standard" of the last few years, there 

 are several exhibits that are well worth attention. 

 We are glad to notice an improvement in the 

 arrangement, each department being kept more 

 distinct than heretofore. 



Zoological work is better represented than any 

 other. Captain F. D. S. Fayrer shows several 

 photographs of the daboia (a' venomous viper), 

 in one of which venom can be distinctly seen 

 hanging from the fangs. As an example of 

 photographic difficulties successfully overcome, the 

 " Flying Sea Gull " of Mr. B. H. Bentley 

 should _ be noticed. There are several sets 

 of prints illustrating progressive changes. The 

 one that will probably be considered the most 

 notable is " A comparison of a jump of one foot in 

 height as executed by a dog and a cat respectively." 

 There are sixteen photographs of each animal show- 

 ing as many stages of the jump, and thev demon- 

 strate that both animals judge with remarkable 

 nicety the rise necessary to clear the obstacle, and 

 that the movement of the legs is the same in both 

 cases. "The Embryology of a Chicken," bv Mr. 

 W. M. Martin, is a series of seventv photographs, 

 one by Rontgen rays, some by transmitted light, 

 and some by a combination of transmitted and 

 reflected light. It is clever and useful work which 

 must have needed considerable patience for its exe- 

 cution. The Zoological Photographic Club has con- 

 tributed a number of very interesting and meritorious 

 photographs, including one bv Mr. Douglas English 

 of the Orkney vole, the last discovered British 

 mammal. 



Mr. R. H. Baskett shows how, by means of a 

 simple original such as a piece of lace or a sprig 

 of forget-me-not or bramble, many designs may be 

 obtained by the use of mirrors as in a kaleidoscope, 

 if the multiplied image is photographed. He says 

 that millions of designs may be obtained for the cost 

 of the plates. A truly amateur's view of the matter 

 in neglecting the cost of the apparatus and the time 

 of the worker ! 



Colour photography is but poorlv represented. 



A basket of fruit by Mr. S. R. Brcw'erton, done by 



the Sanger-Shepherd imbibition process, is a notable 



example, but such fine work has been done by this 



NO. 1822, VOL. 70] 



method that we cannot pass over the background, 

 which if not unfortunate in its tint has not been 

 reproduced with the perfection that we expect. Of 

 the specimens of commercial colour work there is 

 little to be said. What is wanted for exhibition is 

 the original with its reproduction, produced with- 

 out any fine etching or other hand work ; then 

 we shall be able to see what colour photo- 

 graphy pure and simple is capable of, and to 

 judge of its progress. If the trichromatic prints 

 produced by Dr. Jumeaux's process fairly show 

 the capabilities of that process, we can only sav that 

 it is a long way behind other processes. Photo- 

 graphers should notice the " three-colour carbon 

 print " by Mr. J. Gilbert Jackson, as for obvious 

 reasons they are not likely often to have the oppor- 

 tunity of seeing prints produced in this way. The 

 carbon tissue is triply coated, so that the high lights 

 show blue, the half tones, ochre, and the low tones, 

 green. Of course, the colour in the print is in no 

 way dependent on the colour of the object. The 

 interest of the exhibit lies only in the fact that the 

 method has been seriously proposed for practical 

 work. 



A telephotograph of St. Paul's showing a direct 

 magnification of twenty-four diameters demonstrates 

 excellently the usefulness of this kind of work. A 

 number of photomicrographs, some Playertype en- 

 largements, some star maps, and a few other items 

 are all worth examination ; but the most notable of 

 the remaining exhibits is a series of radiographs 

 showing bone diseases by Mr. C. Thurstan Holland. 

 The amount of detail obtained in difficult cir- 

 cumstances is remarkable, and the exhibit is further 

 praiseworthy as forming a connected whole instead 

 of, as we often see, a heterogeneous collection of 

 examples that have happened to turn out well. \\'e 

 regret to notice that there is no apparatus whatever 

 in this section of the exhibition. Probably th" 

 presence of the trade exhibits in the central court 

 is the reason for the disappearance of what used to 

 be one of the main sections, but general exhibits by 

 the trade do not take the place of a classified selec- 

 tion of new apparatus. In the central court will be 

 found new cameras, or modifications of old ones, by 

 several makers, and some new sensitometric apparatus 

 and a recording chronograph by Messrs. Sanger- 

 .Shepherd and Co., besides, of course, a large selec- 

 tion of the various specialities of the exhibitors. 



Of lantern slides there is a fair number, and they 

 appear to be of more than usual interest. .A series by 

 Dr. G. H. Rodman showing how by the use of 

 Rontgen rays the structure of molluscan shells can 

 be shown, and a series of studies in the biology of 

 flowers by Mr. B. H. Bentley, are the most con- 

 spicuous. But we cannot discover when these can 

 be seen properly displayed, for a slide is not made 

 to be looked at, but to furnish an enlarged image on 

 a sheet. It appears that at the lantern lectures, which 

 are given at intervals, other slides are shown. 



PROF. N. R. FINSEN. 

 T^HERE are many records of patient heroism in 

 •'• the history of scientific investigation, but there 

 are few careers in which strenuous work for the 

 alleviation of human suffering has been carried on at 

 greater disadvantage than that of the late Prof. 

 Finsen, of Copenhagen. 



Twenty years ago, he was the victim of a severe 

 attack of rheumatism, which left the heart seriously 

 damaged, and this was followed by disease of the 

 liver and dropsy. Bv the greatest self-denial, and 

 the most careful regulation of his dietary, Finsen 



