30-1 Royal Society ;— 



balanced only by some external pressure. But besides these varieties 

 of heat, depending on the solid, fluid, or gaseous structure of the 

 whole body, there will be another variety, an atomic heat, depending 

 on the essential structure of the compound atoms themselves. It 

 will be least where their monads are most compact, and greatest when 

 they are at greater intervals from each other." 



Surely these numerous assertions can only be regarded as expres- 

 sions of personal conceptions, the correspondence of which to physical 

 realities is proved neither by immediate explanations of phenomena, 

 nor by explanations deduced by mathematical reasoning. There is, 

 for instance, a wide gap which requires filling up, between asserting 

 that each atom revolves about its axis of greatest moment and by its 

 vis viva weakens or destroys the polarity of neighbouring atoms, and 

 explaining how by this action fluidity results. Besides, if the views 

 in the above passage corresponded to realities, the realities would 

 just as much require explanation as the fact of chemical combustion 

 which it was proposed to explain. Nothing therefore is gained by 

 multiplying such conceptions. Science advances in proportion as 

 the explanations of phenomena are reduced to few and definite ideas 

 derived immediately from experiment and observation. Thus Newton 

 added greatly to our knowledge by proving mathematically that the 

 force which produces the motions of planets and satellites, whatever 

 intrinsically it may be, is not different in kind from that which causes 

 a stone to fall to the ground. 



Although we have thought it right to express our dissent from 

 Mr. Birks's theoretical principles, we are ready to admit that his 

 w T ork is not altogether unworthy of a mathematician who gained high 

 distinction in the University of Cambridge. Much care and labour 

 have evidently been bestowed on its composition, and it shows large 

 and accurate acquaintance with the existing state of physical science. 

 Excepting where he is attributing influences to his wonder-working 

 " dual atom/' his theoretical views are generally sensible and dis- 

 criminating. They are not, however, always new. Some of the ex- 

 planations, for instance, contained in the articles in Chap. V., on the 

 relations between Light and Sound, and on Musical Tones and 

 Colours compared, will be found in the Report of the British Asso- 

 ciation for 1834, and in vol. xii. (S. 4) of this Magazine. 



XLII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 233.] 

 June 19, 18G2. — Major-General Sabine, President, in the Chair. 



THE following communications were read : — 

 "On the Photographic Transparency of various Bodies, and on 

 the Photographic Effects of Metallic and other Spectra obtained by 

 means of the Electric Spark." By Prof. W. Allen Miller, M.D., 

 LL.D., V.P. and Treas. K.S. 



In this paper the author pursues an inquiry the commencement 



