On the Heat in the Sun's Rays. 



381 



effect. But the most striking results were obtained by concen- 

 trating the rays with a lens. One was placed in the receiver 

 with its focus directed upon an additional thermometer, the 

 second and third columns in the following table contain the tem- 

 peratures of the air and in the sun, and the fourth, the heat in 

 the focus, while the air in the receiver was heated as before. 

 The atmosphere at the time was not entirely clear. 



No. of obs. 



Temp, of air. 



Temp, in sun. 



Heat in focus. 



1 



76 



82 



104 



2 



78 



88 



114 



3 



80 



90 



120 



4 



84 



96 



130 



5 



90 



102 



138 



6 



100 



110 



148 



7 



104 



114 



152 



The burning glass was then so arranged that being within the 

 receiver its focus was on the outside. The result was as follows : 



No. of obs. 



Temp, of air. 



Temp, in sun. 



Heat in focus. 



1 



44 



50 



60 



2 



51 



60 



60 



3 



58 



68 



62 



4 



62 



72 



62 



5 



73 



83 



60 



6 



96 



106 



58 



Then the burning glass was placed on the outside of the re- 

 ceiver and so arranged that its focus should be on the inside, and 

 the effect was the same as if both glass and focus had been on 

 the inside. 



It will be observed that the effect of the burning glass is sim- 

 ply to increase the results before obtained. Its power depends 

 upon the temperature of the place at which the light is concen- 

 trated. That no heat travels with the light is rendered more 

 manifest. The increased temperature of the rays on the inside 

 had no effect at their focus on the outside. 



The power of the burning glass seems therefore to depend on 

 two considerations : 1st, the amount of light concentrated, 2ndly, 

 the amount of heat on which it acts. 



Those who have heretofore sought its best effects have, it seems 

 to me, too much neglected the latter consideration. Its greatest 

 power is to be obtained by concentrating the greatest amount of 

 light on the highest degree of artificial heat. The combination of 

 the two may perhaps have important practical applications. The 

 chemist may possibly produce new results by adding to the 

 highest resources of artificial heat the powerful agency of con- 

 centrated light. 



The subject is unfinished, and it is my intention to resume it 

 on some future occasion. 



