453 Royal Society : — 



atoms are supposed to be acted upon by heat, light, electricity, 

 affinity, &c.; in short, by agents which are assumed to lie outside 

 the atoms, and as it were adherent to them. 



The discovery of allotropy has made us acquainted with a 

 changeability of the atoms themselves which we had not ima- 

 gined, and that these can undergo such complete alterations, that, 

 for example, a substance in an allotro])ic condition easily com- 

 bines with a certain body, while in another condition it would be 

 perfectly indifferent towards that body. 



An attempt has indeed been made to explain the allotropic 

 conditions of substances by a mechanical hypothesis, that is, to 

 assume the existence of " Arrangemens particuliers des molecules," 

 without, however, stating in what way such an "arrangement 

 particulier " exists, or how such an essential change of the whole 

 properties of a body can be caused by it. 



Such attempts at explanation are, in my opinion, of little ad- 

 vantage to science; and I consider it advisable rather to say 

 nothing about the obscure cause of allotropy than to build up 

 hypotheses, which themselves are founded upon an hypothesis. 



However unintelligible the phsenomenon of allotropy may at 

 present appear to us, so much is evident, that it has a great sig- 

 nificance for theoretical chemistry; and I cannot avoid again 

 remarking, that, in my opinion, the next considerable step in 

 this science will consist in making out the influence which the 

 allotropic modifications of elementary substances exert upon their 

 chemical deportment, and especially upon chemical decomposi- 

 tions and combinations. And I think, therefoi'e, that our insight 

 into the processes of fermentation, and into so many other che- 

 mico-physiological processes and changes of mattei", will only 

 emerge from its present imperfect condition, and take the shape 

 of real knowledge, when the connexion indicated between allo- 

 tropy and chemistry is better and more thoroughly investigated 

 than at the present day. 



LXI. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued fi-om p. 384.] 



June 19, 1856. — The Lord Wrottesley, President, in the Chair. 



THE following communications were read : — 

 " Description of an Instrument for registering Changes of Tem- 

 perature." By Balfour Stewart, Esq. 



It lately occurred to the author that advantage might be taken of 

 the capillary action of mercury to construct an instrument similar to 

 a thermometer, but in which the mercury should expand from heat 

 only in one tube, and contract from cold only in another. Accord- 



