354 CALORIFICATION. 



3. Mr. Davy varied Mr. Cavallo's experi- 

 ments ; the result, however, was found to be 

 uniformly the same. He took six pieces of 

 copper, of equal dimensions, the upper surfaces 

 of which he painted white yellow red 

 green blue and black : the opposite, or 

 dark side, he smeared over with lard, or cerate, 

 which he previously ascertained to melt when 

 heated to the degree of 76* of Fahr.: he placed 

 them in such a manner, as that the painted sur- 

 face only.was exposed to the rays of the sun 

 he invariably found, that the cerate attached to 

 the white bulb, was the longest time in melt- 

 ing, and that the rapidity of the liquifaction 

 gradually increased, from the yellow to the 

 red, from the red to the green, from the green 

 to the blue and black. 



Dr. HERSCHELL made experiments of a si- 

 milar nature, with the same result ; he was led 

 to perform them, in consequence of the neces- 

 sity he was under, at the time he was making 

 observations on the sun, by means of teles- 

 copes, of making use of colored glasses, to pre- 

 vent the ardor of the rays from injuring his 

 eyes. He found, that when the glasses were 

 of a color, so deep, or dark, as to interrupt 

 the light, they very soon cracked and broke 

 in pieces. This circumstance induced him to 

 examine the heating power of the different co- 

 lored rays ; for which purpose, he made each of 



