M. MELLONI ON THE POLARIZATION OF HEAT. l7l 



the different calorific rays, and in measuring their indices of 

 polarization for a given incidence with the greatest exactitude, 

 we shall only add a new element to the science of radiant heat, 

 which mil separate, by a few fractions of a degree, the inchna- 

 tions actually known, at which the different species of rays give 

 the same quantity of polarization. But all these species being 

 susceptible of complete polarization, will still, notwithstanding 

 these little distinctions, be of the same polarizable nature. 



Heat then is polarized absolutely, like light, by refraction and 

 reflection ; a conclusion which fully confirms the theoiy deve- 

 loped in the first part of this memoir, to show how the phaeno- 

 mena of polarization may take place in the interior of tourma- 

 lines without the possibility of perceiving them outwardly*. 

 Indeed, it may be remembered that certain species of tourmalines 

 give a calorific polarization, which is either total, incomplete, or 

 null in appearance, according to the quality of the heat em- 

 ployed. But we have just seen that all the calorific rays are 

 equally polarizable : there exists, therefore, in the tourmaUnes, 

 a cause which sometimes conceals, and sometimes exhibits the 

 polarizing action. This cause can only be double refraction, 

 which always produces two superposed pencils, equally intense, 

 but differently polainzed, in plates divided pai-aUel to the axis of 

 crystallization. When the action of the touraiahnes manifests 

 itself, one of these pencils is completely absorbed, and the other 

 remains alone and exhibits its proper direction of polarization ; 

 in the opposite case, the two pencils undergo an equal absorp- 

 tion, and issue together completely neutralized with regard to 

 polarization. Now if in the latter case the emergent heat re- 

 sembles ordinary heat, the second pencil, which was previously 

 absorbed, must necessarily be polarized at right angles to the 

 other ; its polarization must also be complete, for it is in that 

 state that the first pencil of heat is separately exhibited. 



The production of two calorific pencils in bi-refractive 

 media, and their rectangular polarization, is also inferred from 

 another experiment exactly analogous to those performed in 

 optics to show the action which bodies possessing double refrac- 

 tion exert upon polarized Ught. 



If a ray of light, reflected by a mirror of black glass, at an 

 angle of 30° 25', traverse perpendicularly a lamina of sulphate 



* Vol. Ixi. p. 408, of the Annales tie Chim. et de Phys. [or Scient. Mem. 

 vol. i. p. 315. Edit.] 



