336 EADIANT HEAT. 



some general remarks on these results as related to those of Seebeck 

 on prismatic dispersion. 



A supplement to the last paper was presented by the same author 

 to the Academy, April 21, 1834, entitled " New Researches on the 

 immediate Transmission of Radiant Heat through different Solid and 

 Liquid Bodies." It is published in the Ann. de Chimie, lv, 337, and 

 translated in Taylor's Scientific Memoirs, Part I, p. 39. 



The author first investigates " the modifications which calorific 

 transmission undergoes in consequence of the radiating source being 

 changed." 



He employs four sources of heat. 1. A Locatelli lamp. 2. Incan- 

 descent platina. 3. Copper heated by flame to about 730° Fahren- 

 heit. 4. Hot water in a blackened copper vessel. The heat from 

 each of these sources was first compared as transmitted through plates 

 of glass of different thicknesses, from .07 millims. to 8 millims. The 

 results are given in a table, from which it appears that with copper 

 and hot water the diminution of effect is rapid, with an increase o* 

 thickness in the screen; with water it is nothing be} T ond a thickness 

 of .5 mm. A second table gives results for about 40 solid media of 

 different kinds of the same thickness; most of them were wholly im- 

 pervious to dark heat; the most remarkable exceptions being fluate 

 of lime and rock salt. 



In another table are the results with black glass and black mica; 

 these substances, though diathermanous to the lamp and incandescent 

 platina, are wholly impervious to the rays from hot water, and nearly 

 so to those from heated copper. 



The discovery of the entire diathermancy of rock salt has been 

 before referred to, and has furnished the means of prosecuting the 

 author's yet more remarkable researches on the Refraction of Heat. 



To this important point M. Melloni devotes a portion of the same 

 memoir. After a sketch of previous attempts to establish this prop- 

 erty, he describes his successful experiment by concentrating to the 

 focus of a rock-salt lens the rays of 'dark heat from hot copper and hot 

 water. A similar lens of alum produced no effect. This proves that 

 the effect is not due to the mere heating of the central part of the 

 lens. 



He next advances to the refraction of heat by a rock-salt prism; 

 describing an apparatus for the purpose. That the effect is not due 

 to secondary radiation is shown by turning the prism on its axis into 

 a different position, when no effect is produced. 



He then discusses the "properties of the calorific rays immediately 

 transmitted by different bodies." Under this head are detailed one 

 of the most remarkable species of effects which the whole range of 

 the subject presents. 



The rays of the lamp were thrown upon screens of different sub- 

 stances in such a manner that either by changing the distance, or by 

 concentration with a mirror, or a lens of rock salt, the effect trans- 

 mitted from all the screens was of a certain constant amount. This 

 constant radiation was then intercepted by a plate of alum, and it was 

 found that very different proportions of heat were transmitted by the alum 



