24 



On the Injluence of Color on Radiation. 



The radiating power being greater, as the time of cooling is less, 

 we have the order of radiating power of the different colored substan- 

 ces, as follows : white, red, brown, orange, black, green. Omitting 

 in this enumeration the blackened surface of the red oxide of lead, 

 which had passed in thickness the maximum radiating thickness, and 

 is only comparable with the result which precedes it. The change 

 of color effected by changing the surface sulphuret of lead, (black or 

 rather brown) increases the radiating power in the ratio of 1.03 to 1, 

 which is within the average of error. 



The following results given in order of time, and reduced by the 

 standard, were obtained with cylinder No. 2. 



The variety of color is here small ; the radiating powers rank, 

 blueish green, dark brown, white, blue ; omitting the second exper- 

 iment with the carbonate of lead which is only comparable with the 

 one in which the surface was blackened by hydro sulphate of potassa. 

 Comparing these two results the change of surface appears to have 

 increased the radiating power in the ratio of 1.04 to 1. 



The coatings applied to cylinder No. 3, were more varied than 

 those of either of the foregoing. 



