154 M. MELLONl ON THE POLARIZATION OF HEAT. 



The quantity of heat which reaches the thermoscope, at a 

 given inchnation of the piles, diminishes in proportion as the 

 number of the laminae increases. In order to operate as much 

 as possible in the same circumstances, it appeared desirable to 

 render the largest galvanometrical deviation produced in each 

 of the eight series nearly constant. To effect this, I employed 

 a small spherical metallic mirror, making the centre of curvature 

 coincide with the middle of the flame ; the concavity was turned 

 towards the lens of rock salt. In this situation the calorific 

 rays thrown off in the direction opposite the lens, were reflected 

 upon themselves ; and, being mixed with the heat thrown di- 

 rectly upon the lens by the flame, increased the intensity of the 

 pencil parallel to the axis. I commenced each series by blacken- 

 ing the whole surface of the mirror by the flame of a resinous 

 taper ; then by partly removing the lamp-black with a linen 

 cloth I gradually restored the metallic lustre upon a portion of 

 its surface, increasing its extent until the intensity of the heat 

 which reached the thermoscope at that inclination of the piles 

 at which the maximum effect was obtained, had nearly attained 

 the value of the largest galvanometrical de^^ation adopted, which 

 was from 35° to 37°. It is almost superfluous to add, that 1 

 afterwards left the apparatus in the same state during the whole 

 series of experiments having relation to the same pair of piles, 

 so that all the quantities contained in each table may be com- 

 pared together. 



The titles inscribed at the head of each column sufficiently 

 denote the objects to which the series of numbers which they 

 contain relate. The first gives the angle under which the pair 

 of piles meets the calorific pencil, which is measured from the 

 surface. The second and fourth indicate the arcs, reckoned 

 from 0°, described by the index of the galvanometer at the ini- 

 tial effect, when, in establishing the radiating communication 

 with the source, the heat arrives upon the thermoscope, through 

 the piles, in the two directions, parallel and perpendicular, of 

 their planes of refraction : each of the numbers they contain has 

 been estabUshed from a sei'ies of ten observations. The third 

 and fifth columns contain the intensities of the forces corre- 

 sponding to the arcs of the second and fourth. The last column 

 comprehends the quantity of heat polarized in 100 transmitted 

 rays when the planes of refraction are parallel ; which quantity 



