M. MELLONI OiN THE POLARIZATION OF HEAT. 153 



solely by the heat directly transmitted by the piles inclined 45° 

 upon the axis of radiation, whatever, in other respects, may be 

 the particular position which they affect around it. 



Now leave one of the drums at 0°, and place the other at 90°, 

 or 270°: the common inclination of the piles upon the axis 

 undergoes no alteration, but the planes of refraction deviate 

 from their parallelism, and take a perpendicular direction ; so 

 that one of them, for example, being horizontal, the other ne- 

 cessarily becomes vertical. Now, upon transmitting the invari- 

 able radiation of the lamp through our ten laminae thus dis- 

 posed, we shall no longer have, as before, 35°*92 of deviation, 

 but only 28°'54. There is then a very distinct diminution in 

 the quantity of heat that reaches the thermoscope. According 

 to the two preliminary experiments just described, this diminu- 

 tion can only be attributed to an effect of polarization. 



The arcs of 35°-92, and 29°-54*, described by virtue of the 

 primitive impulsions of the galvanometrical index, correspond 

 to forces of 32-10 ; and 24-95. Dividing the difference of these 

 two quantities by 32-10, and multiplying the quotient by 100, 

 we have 22-06, a number which evidently represents the quan- 

 tity of heat polarized by the 'pair of five laminae, expressed in 

 hundredths of the quantity transmitted when the two planes of 

 refraction are parallel. 



But this result was obtained at an incidence of 45°. In what 

 direction is the variation of the polarizing action of the laminae, 

 when the angle which they form with the calorific rays is dimi- 

 nished ? Is the proportion of heat polarized notably increased 

 with the number of the laminee ? What degree of polarization 

 may be reached by the concurrence of these two elements? 



I have made several series of experiments, in order to resolve 

 these different questions. Their results are laid down in eight 

 tables, which we proceed to notice, first endeavouring clearly to 

 explain the circumstances under which they were made. 



I combined successively my eight piles, singly, two and two, 

 and three and three ; I thus formed of them eight pairs, com- 

 posed of 3, 5, 10, 15, 20, 25, 30, and 35 laminae. Each pair 

 was then raised upon the apparatus, and exposed to the calo- 

 rific flux of the lamp, in the parallel and perpendicular direc- 

 tions of the planes of refi-action, and at different inclinations. 

 [* So in the original] 



