324 Dr. Herschel's Experiments on the solar, and 



E, is the hole through which the heat passes to the ther- 

 mometers. 



No. 1 and No. 4, are the thermometers. 



F, is a prism, which, in the 6th experiment, is to be placed 

 in the room of the mirror D. 



Plate XII. Fig. 4. 



A, is the board that holds the apparatus used in the 7th 

 experiment. 



B, The prism. 



C, The spectrum, thrown partly on the paper with parallel 

 lines, and partly on one of the small tables which support the 

 board. 



D, The mirror which reflects the rays of heat sideways. 

 No. 1, The thermometer which receives the reflected rays. 

 No. 2, The standard thermometer. 



Plate XIII. Fig. 1. 



A B, is the front which, in the 9th experiment, is put close to 

 the flat side of a heated iron stove. 



C, is the mirror. 



D, The feather-edged slip of deal, on two pins. 



No. 2, The thermometer which receives the rays condensed 

 in the focus of the mirror. 



No. 3, The standard thermometer. 



E, A small screen tied to No. 3, to guard it from reflected 

 heat. 



Plate XIII. Fig. 2. 

 A, The lens in the apparatus used for the 12th experiment. 

 No. 2, The thermometer placed in its focus. 



