306 Dr. Herschei/s Experiments on the solar, and 



make room for the balls to be freely exposed. That of No. 2 

 was in the axis of the mirror; and the ball of No. 3 was screened 

 from the reflected rays, by a small piece of pasteboard tied to 

 the scale. The small ivory scales of the thermometers, with the 

 slip of wood at their back, which however was feather-edged 

 towards the stove, intercepted some heat; but it will be seen 

 presently that there was enough to spare. When my stove was 

 of a good heat, I brought the apparatus to a place ready pre- 

 pared for it. 



No. 2. No. 3. 



In the Focus. Screened. 



o' 52- 52 



1 91 53 



Here we find that, in one minute, the invisible culinary heat 

 raised the thermometer No. 2, 39 degrees; while No. 3, from 

 change of temperature, rose only one, notwithstanding its 

 exposure to the stove was in every respect equal to that of 

 No. 3, except so far as relates to the rays returned by the 

 mirror; and therefore, the radiant nature of these invisible rays, 

 their power of heating bodies, and their being subject to the 

 laws of reflection, are equally established by this experiment. 



lotb Experiment, Reflection of the invisible Rays of Heat of a 

 Poker, cooled from being red-hot till it could no longer be 

 seen in a dark Place. 



The great abundance of heat in my last experiment, would 

 not allow of its being carried on without injury to the thermo- 

 meter, the scale of which is not extensive ; I therefore placed a 

 poker, when of a proper black heat, at 12 inches from the steel 

 mirror,* and received the effect of its condensed rays upon the 



* See Plate XII. Fig. 1. 



