210 Professors Redtenbacher and Liebig 



the lines of light being affected, the luminous material be- 

 coming diffused in the paper. 



The fact, therefore, that a given compound remains un- 

 changed even in the direct rays of the sun, is no proof that 

 light cannot decompose it ; it may reflect or transmit the ac- 

 tive rays as fast as it receives them. It results from this, that 

 optical forces can control and even check the play of chemical 

 affinities. Whilst thus it appears that there are points of 

 analogy between this chemical agent and. radiant heat, we 

 must not too hastily infer that the laws which regulate the one 

 obtain exclusively also with the other. As is well known, 

 there are striking analogies between radiant heat and light, 

 but there are also points of difference, the convertibility of 

 heat of one degree of refrangibilily to another does not oc- 

 cur with light; there are also dissimilitudes in the phaeno- 

 mena of radiation and its consequences. I do not doubt, that 

 what has been communicated in this memoir, will, by the re- 

 searches of others, be greatly extended ; but it is not to be ex- 

 pected that a complete parallel can be run between radiant 

 heat and the chemical rays, any more than between radiant 

 heat and light. 



From the phenomena of the interference of these rays, of 

 the sensitiveness or non-sensitiveness of the same chemical 

 compound being determined merely by the fact of its thick- 

 ness or thinness, these, and many other similar results, ob- 

 viously depending upon mechanical principles, it seems to me 

 that very powerful evidence may be drawn against the ma- 

 teriality of light, and its entering into chemical union with 

 ponderable atoms. Those philosophers who have endea- 

 voured to prove the undulatory theory, will probably find in 

 studying these subjects cogent evidence in favour of their 

 doctrines. 



XXXI. On the Atomic Weight of Carbon. By Professors 

 Redtenbacher of Prague^ and Liebig ofGiessen*, 



IN the analysis by combustion of organic substances which 

 contain carbon and hydrogen, the observation has fre- 

 quently been made of late years, that the weight of the ele- 

 ments separately found by experiment, actually exceeds the 



* Translated from the original German by Dr. J. H. Gilbert; and com- 

 municated by the Chemical Society, having been read before the Society, 

 May 8th, 1841. 



An abstract of Dr. Marchand's paper on the same subject will be found 

 in the Proceedings of the Society, to be given in our next Number. 



