BY JAMES TOLSON, ESQ. 57 
reflecting power, because the two are not exactly comple- 
mentary, still from experiments made by Dulong and Petit 
there is strong evidence that they are so. All experiments 
made for the purpose show that those substances which are 
good radiators are also good absorbers, and it is therefore 
concluded that the radiating power is equal to the absorbing 
power for the same body, and for the same difference 
between its temperature and the temperature of the sur- 
rounding medium. It follows, therefore, that causes which 
modify the absorbing powers will modify the radiating 
powers also; and as the reflecting power varies in an 
inverse manner to these, whatever increases it diminishes 
the radiating and absorbing power, and wice versa. 
The following table, taken from the work of M. Ganot, 
gives the relative radiating and absorbing power of various 
substances as compared with lampblack; lampblack being 
taken as the standard of comparison, as it absorbs all the 
rays falling upon its surface, reflecting none. 
Lampblack - - 100 Tarnished Lead - 45 
Whitelead - - 100 Polished Lead - 20 
Raper; = - - 98 Polished Iron - 15 
Ordinary White Glass go Tin, Copper, Gold, ) 
Ismglass -... - .- 80 | ots Sole tog We 
From experiments made by Balfour Stewart on radiant 
heat, he found that— 
‘“‘ Radiation goes on in the interior of a body just as much as at 
the surface, and that in the interior of substances, as well as in air 
Or in vacuo, a stream of radiant heat is constantly passing and 
repassing in all directions ; and ina case of constant temperature, 
as this stream of heat passes any layer of particles, it is just as much 
diminished by the absorbing action of these particles as it is 
recruited by their radiation, so that the stream flows on virtually 
unchanged both in quantity and quality, until it at last reaches the 
surface.” 
And that, according to the theory of Prevost— 
“rst. If an enclosure be kept at a uniform temperature, any 
substance surrounded by it on all sides will ultimately attain that 
temperature. 
“2nd. All bodies are constantly giving out radiant heat, at a 
rate depending upon their substance and temperature, but inde- 
