Dr. Herschel's Experiments, &c. 285 



all the spectrum, except the vanishing last quarter of an inch, 

 which served as a direction, passed down by the edge of the 

 stand, and could not interfere with the experiments. I had also 

 now used the precaution of darkening the window in which the 

 prism was placed, by fixing up a thick dark green curtain, to 

 keep out as much light as convenient. 



The thermometers being perfectly settled at the temperature 

 of the room, I placed the stand so that part of the red colour, 

 refracted by the prism, fell on the edge of the paper, before the 

 thermometer No. 1, and about half way, or 1^ inch, towards 

 the second : it consequently did not come before that, or the 

 3d thermometer, both which were to be my standards. During 

 the experiment, I kept the last termination of visible red 

 carefully to the first line, as a limit assigned to it, by gently 

 moving the stand when required ; and found the thermometers, 

 which were all placed on the second line, affected as follows. 



No. 1. 







No. 2. 



No. 3 



45 



- 



- 



45 



44 



49 



- 



- 



45 



44 



51 



- 



- 



44| 



44 



5°£ 



- 



- 



43i 



431 



Here the thermometer No. 1 rose 6| degrees, in 10 minutes, 

 when its centre was placed \ inch beyond visible light. 



In order to have a confirmation of this fact, I cooled the 

 thermometer No. 1, and placed No. 2 in the room of it : I also 

 put No. 3 in the place of No. 2, and No. 1 in that of No. 3 ; 

 and, having exposed them as before, arranged on the second 

 line, I had the following result. 



