1835.] and Analysis of the Vanadiate of Lead. 45 



or Dichloride of lead . 16-767 

 Divanadiateoflead . 83*073 

 Insoluble matter . . 0*160 



100*000 



equivalent to 



1 atom Dichloride of lead, and 

 4 atoms Divanadiate of lead 



and the formula, Pb* Ch. + 4 Pb* V. 



Article VI. 



Transmission of Heat through different Solid and Liquid 

 Bodies. By M. Melloni. Ann. de Chimie, lvi. 



Radiating heat passes immediately, and in greater or less 

 quantity, through a certain class of solid and liquid bodies. 

 This class is not precisely identical with diaphanous bodies, 

 as opaque plates or such as possess only a slight trans- 

 parency, are more diathermanous, that is to say, more per- 

 meable to radiating heat than other plates completely 

 transparent. 



Different species of calorific rays exist, which are all 

 emitted simultaneously, and in different proportions by 

 burning bodies. Rock-salt formed into a plate, and suc- 

 cessively exposed to rays of the same force, proceeding from 

 different sources, transmits immediately, the same quantity 

 of heat. A plate of every other diathermanous substance, 

 placed in the same circumstances, transmits quantities more 

 feebly in proportion as the temperature of the radiating 

 source is less elevated ; but the differences of each trans- 

 mission diminish in proportion to the thinness of the plate. 

 From whence it follows, that the different rays of heat from 

 different sources are intercepted in greater or less quantity, 

 not on the surface, and from an absorbing power, which 

 varies with the temperature of the source, but even in the 

 interior of a plate, by an absorbing power similar to that 

 which preserves certain kinds of light in a coloured medium. 



We arrive at the same conclusion in considering the loss 

 which the" rays of heat from a source of high temperature 

 sustain in passing through the successive elements of which 



