on the terrestrial Rays that occasion Heat. 323 



EXPLANATION OF THE FIGURES. " 



See Plates XII. XIII. XIV. XV. and XVI. 



Plate XII. Fig. 1. 



Shews the arrangement of the apparatus used in the ad 

 experiment. 



A, is the small mirror with its adjusting screws m, n. 

 No. 2, is the thermometer in the focus of the mirror. 

 No. 3, The assistant thermometer. 



B, A small screen for the thermometer No. 2. 



C, The candle. 



D, The poker which, in the 4th and 10th experiments, is to 

 be placed in the situation of the candle ; the rest of the appa- 

 ratus being brought nearer to it. 



Plate XII. Fig. 2. 



Shews the apparatus used in the 3d and 8th experiments. 

 ' A, The mirror. 

 No. 2, The thermometer. 

 B C D, A desk adjustable to different altitudes. 



E, The prism receiving the sun's rays through an opening 

 in the window shutter F. 



Plate XII. Fig. 3. 



AB, is the front of the apparatus, which, in the 5th experi- 

 ment, is exposed to the fire of the chimney. 



C, is the opening in the front plate AB, for the admission of 

 heat. 



D, is the small mirror which reflects the rays of heat. 



