232 EECENT PROGEESS IN RELATION TO THE THEORY OF HEAT. 



tlio principal sections of the two spars are perpendicular. Here, then, we have 

 the experiniencal demonstration of the polarization of obscure heat. 



Let us next place hetween the trough and the second spar a lamina of quartz, 

 the thermo-electrie battery manifests heat anew, just as if, without interposing the 

 quartz, we had caused the first spar to turn by a certain angle. It is usual to 

 say that the ordinary pencil which issues from the spar is polarized in the prin- 

 cipal section, and that the transmission of this pencil through the quartz causes 

 the plane of loolarization to revolve. To conclade the experiment, we cause the 

 first spar to turn until the ordinanf-ordinarij pencil which encounters the battery 

 is extinguished anew, and the angle of this rotation measures the rotation of the 

 plane of pohxrization. 



The perfect resemblance of a luminous and a calorific ray has led to the infer- 

 ence that the forces which are at play in the two radiations phxce matter in a simihar 

 state of movement. Would we figure to ourselves a suite of movement capable 

 of producing all the phenomena of light, we have but to imagine an infinitude of 

 particles situated upon the ray and oscillating from one side to the other of an 

 intermediate position, like the particles of a chord which yields a sound ; two 

 consecutive particles act one on the other in such a way that everj' modification 

 of movement in the one induces a determinate modification in the other. While 

 a particle executes a complete oscillation the movement is transmitted to a certain 

 distance which is called length of wave. Here we have the point of departure 

 of the theory of undulations ; the same hypothesis is applicable to heat. 



From the fact that the propagation of heat and light takes place as well in a 

 vacuum as through ponderable bodies, tho above hypothesis must be thought 

 incomplete unless it be supposed in addition that the matter which transmits the 

 undulations is different from ponderable matter; to the former, therefore, has been 

 given the name of ether. Were this vibrating matter even of the same nature 

 Avith the matter of ponderable bodies, it would still be useful to employ a special 

 word to indicate that it is in a particular state, capable of ]>ropagating light; as 

 the purpose in using it is to represent to ourselves the possible mechanism of the 

 phenomena, we should, above all, seek simplicity of language, and the use of 

 the phrase luminous etJter satisfies tliis condition. 



It may naturally be asked whether there is a calorific ether distinct from the 

 lumi7ious ether, or whether one sole ether is sufiicient for the mechanical repre- 

 sentation of the radiation of light and of that of heat. Only one, it is evident, 

 should be admitted, if that suffices for the explanation of all the known facts, and 

 the question here relates to facts Avhich take place in the material world, outside 

 of ourselves and independently of our sensations. To the well-known researches 

 of MM. Jamin, Masson, and Delaprovostaye, which corroborate the hypothesis 

 of a single etlK3r, we should now add the late investigations of M. Desains on the 

 rotation of the plane of polarization of the rays of obscm-e heat in passing through 

 quartz. 



When the question relates to luminous rays we know that the rotations of the 

 plane of polarization are inversely proportional to the squares of the lengths of 

 wave. If there be luminous rays having a length of wave four times greater 

 than that of the violet rays, their rotation, according to this law, would be 16 

 times smaller than the rotation of these last. Now, MM. Delaprovostaye and 

 Desains had heretofore established that calorific rays and luminous rays of the 

 same length have the same rotation. And now M. Desains shows us that tho 

 rays of obscure heat satisfy the law as enunciated, and among these rays there are 

 such as have, in fact, a rotation 16 times less than that of the violet, and a length 

 of wave lour times greater. 



Instead of assuming that two like systems of waves propagate, the one heat, 

 the other light, while they undergo the same modifications bj' reflection and 

 refraction, is it not more simple to admit but a single system, the longest waves 

 producing the effectsof heat, and the shortest those of light ? Such is the import 



