ON HEAT AND LIGHT. 167: 



As the quantities of light falling on both were equal, the The denfities of ^ 

 denfity of the light at the furface of the refervoir A was to the \ x ^St$o{ 

 den.fi ty of that at the furface of the refervoir B, as the fquare light were there- 

 of 24 to the fquare of 6, or as 16 to 1. forc as l6 t0 * 5 



I imagined, that, if the quantity of heat, which a given 

 quantity of light is capable of exciting, depended anyway on 

 its denfity, as the denfities were fo different in this experiment, 

 I could not fail to difcover the fact by the difference of time, 

 which it would require to raife the two thermometers the fame 

 number of degrees. 



Having continued the experiment more than an hour, on a but beth the 

 very fine day, when the fun was near the meridian and Seated fo"q Ua i 

 ihone extremely bright, I did not find, that one of the refervoirs times. 

 was heated perceptibly quicker than the other. 



Erperiment II. 



I placed the refervoir of heat A ftill nearer the focus of the Experiment 

 lens, in a fituation where the folar fpedrum was only 4| lines ^^"ofthc 1 *'" 

 in diameter, and where blackened paper caught fire in two or fpots were as 

 three feconds; and I removed the refervoir B itill farther from 4l t0 a 7» 

 the focus, advancing it forward till the diameter of the fpeclrum 

 was two inches three lines. 



The denfities of the light at the furfaces of the refervoirs in The denfities 



this experiment were as 32 to 1 . of the u S ht wer * 



as 32 to 1. 

 The temperature of the refervoirs, as well as that of the at- 



mofphere, at the beginning of the experiment, was 54° F. = 



The refervoir A, after having been expofed to the action of The denfeft 



very intenfe light near the focus of the lens for twenty-four bght afforded 



. J ,. ,. . r , 1 i. rather lefs heat, 



minutes forty leconds, was railed to the temperature of 80° F. 



= 21°4.R. 



The refervoir B, which was much farther from the focus of 

 its lens, was railed to the fame temperature, 80° F. a little 

 more quickly, or in twenty-three minutes forty feconds. 



To raife the temperature of the refervoir A to 100° F. =■ 

 30° •§ R. it was neceflary to continue the experiment for one 

 hour fifteen minutes ten feconds, reckoning from the com- 

 mencement of it ; but the refervoir B reached the fame tem- 

 perature in one hour twelve minutes ten feconds. 



The progrefs of this experiment from the beginning to the 

 end is exhibited in the following table : 



Increafes 





