RADIANT HEAT. 335 



through Solid and Liquid Bodies," was presented to the Academy of 

 Sciences at Paris, Feb. 4, 18o.">, and published in the Ann. de Chimie, 

 No. liii, p. 1: a translation of it is given in Taylor's Scientific 

 Memoirs. Tart I. 



The author commences with a slight sketch*of the researches of 

 previous experimenters, but omits to notice any distinctions between 

 the characters of the heat from different sources, or the different 

 kinds of heat from one and the same source, when luminous, espe- 

 cially as indicated by my experiments published in the Phil. Trans. 

 for 1825. 



He then proceeds to some "general considerations on free trans- 

 mission of caloric through bodies, and the manner of measuring it by 

 means of the thermo-multiplicr." This, in fact, constitutes a sup- 

 plementary and more enlarged portion of his former researches. He 

 goes into extensive details on the precautions necessary to be used in 

 such investigations; especially for guarding against the interference 

 of secondary radiation: as this changes with the change of place of 

 the screen, he thus allows for its effects. He also gives some general 

 observations on the use of the galvanometer, and the correct estima- 

 tion of the forces acting upon it. 



The next subject of inquiry is the effect due to " the polish, thick- 

 ness, and nature of the screens." The source of heat being a lamp, 

 screens were employed of glass rendered of different degrees of 

 opacity by grinding, &c. ; and the effects by transmission through 

 them were found to be in proportion to the transparency, or that the 

 heat follows the same proportion as the light. 



The effect of liquids between glass plates was then tried; and more 

 rays were found to be absorbed in proportion to the increase of thick- 

 ness. Different numbers of glass screens were also employed in com- 

 bination; the same conclusion also held good. 



The results with a numerous series of screens of various media, 

 solid and liquid, were then tried, and are stated in a series of tables: 

 Table I. Various kinds of uncolored glass. 



Table II. Liquids: to give a general sketch, the order of trans- 

 mission was as follows, beginning with the greatest: 



Carburet of silver. 



Chlorides. 



Oils. 



Acids. 



Water. 

 Table III. Crystallized bodies, transparent and opaque; the results 

 follow no relation to transparency: the following is the general order: 



Rock salt. 



Various crystals. 



Alum. 



Sulphate of copper — no effect. 

 Table IV. Colored glasses. Red and Violet transmitted most — 

 yellow, green, and blue, least — heat. 



The author concludes, in general, (the source being a lamp.) that 

 the diathermancy is not proportional to the transparency; and makes 



