276 Mb KELLAND, ON THE MOTION OF 



or, omitting the first term on the principle above stated, and putting 

 for ^/3' and ^7" their vahies b cos (ut — A-x) c .cos {ut — kx + A), it becomes 



= R {b' cos- {itt—kx)i-c^ COS' {ut—kx + j4)\ 



at 



= R — ^— + -^ {A' cos 2(M^-/i-x)+c'cos 2{ut-kx+A)} ; 



til Ji 



... ^ = R.~^ _t^ ?Lij,^ COS 2 {ut-kx) + c sin 2 {ut-kx + A)\ 



= R — - — . t omittmg the reciprocatnig part, 



da 

 and supposing -^ = 0, when t = 0; 



hence, when the medium is of this kind, there will be a transmission 

 depending on the motion of vibration. 



Tluis it appears that the quantity of one substance A, which enters 

 a medium, depends, cateris paribus, on the intensity of the undulation 

 excited in the particles without the medium. At the same time, a 

 quantity of the other substance B is withdrawn from the medium, 

 and retires to supply the place which the former has left. 



43. The only doubt, which I can perceive, of this being a sufficient 

 explanation of the coincidence of phenomena, which require consider- 

 ations of an undulatory, as well as of a corpuscular, nature arises from 

 the apparent smallness of the term and the consequent smallness of 

 the transmission. 



It would appear, from the recent experiments of Professor Forbes 

 on the Polarization of Heat, that some such terms must enter from 

 whatever considerations they may be deduced. It will, perhaps, with 

 some shew of justice, be objected to the above statement, that all 

 that has been attempted is, to shield ourselves from the necessity of 

 accounting for Polarization of Heat, by referring to its parallel in 

 the absorption of light. 



