270 THE SELECTIVE PHOTOMETER. [MEMOIR XVIII. 



Lights, E, F, set at the opposite ends of the box, A B, 

 may therefore be compared as regards their photographic 

 intensity, the calculations being made by the common 

 photometric law. And by changing the liquid in the 

 absorbing trough, g h, any radiations may be selected 

 for examination. The instrument may therefore be des- 

 ignated as " the selective absorption photometer." 



From the facts presented in this and the preceding 

 paper, as conveying the modern conception of the rela- 

 tion of luminous and calorific radiations, it may be con- 

 cluded that the thermometer with a blackened bulb is 

 an absolute photometer, and that, in accordance with the 

 principles set forth, many other selective photometers and 

 thermometers may be devised. 



