M. MELiLONI ON THE POLARIZATION OF HEAT. 183 



In conclusion, these two great agents of nature, and the mo- 

 difications which they undergo from the action of ponderable 

 matter, are governed by similar laws, while their rays move 

 freely. Numerous differences are manifested as soon as the 

 progress of the two radiations suflfers any interruption what- 

 ever, either at the surface, or in the interior of bodies. 



