on the terrestrial Rays that occasion Heat. 325 



B, The screen with an aperture for admitting the rays of 

 heat.- 



C, The eccentric pivot for turning away the lens. 



D, The candle. 



Plate XIV. 



A, The burning lens, covered ; with the prismatic spectrum 

 thrown upon an opening, left for it, in the pasteboard cover of 

 the 13th experiment. 



No. 3, The thermometer placed in its focus. 



B, The prism. 



C, Semicircular cover, used in the 17th and 18th experiments, 

 instead of the one with a square hole. 



Plate XV. 



A, The burning lens of the 14th experiment. 



B, The fire in the chimney. 



No. 1 , The thermometer in the focus of the lens. 

 No. 4, The standard thermometer. 



C, The hole through which the rays of heat pass to No. 1. 



D and E, Two holes, between which the ball of the thermo- 

 meter No. 4 is screened from the direct rays of the fire ; while 

 free access is given to the heat which may affect the tempera- 

 ture of the place. 



Plate XVI. Fig. 1. 



A, The iron cylinder, stuck upon its handle, as it is used in 

 the 15th and 19th experiments. 



B, The lens. 



C, The screen with an opening in it. 



No. 2, The thermometer in the focus of the lens. 



