On the Heat in the Sun's Rays. 379 



i 



some in amount from the different degrees of brightness in the 

 sun. The change in the temperature of the air was still to be 

 added, and the conclusion seemed to be irresistible, that the sun's 

 rays in passing into the heated room acquired a temperature that 

 they did not derive from the sun. 



The experiment was next repeated with different temperatures 

 of the room, and it was found that the intensity of the rays de- 

 pended upon the heat of the room. Indeed in the coldest 

 weather in winter I could impart to them a power which belonged 

 to a summer's sun. 



At a later period when the circumstances were changed and 

 the heat on the outside had become greatest, the indications of 

 the instrument were reversed. The high temperature of the 

 summer rays was in a great measure lost or dissipated on enter- 

 ing into a cool room. There they had no greater power than 

 had been found at similar temperatures in the winter. 



For the purpose of a more accurate investigation of the sub- 

 ject, I procured a glass shade or receiver about ten inches in di- 

 ameter and twenty-two in height. A copper base was adapted 

 to it with a groove around the outer edge into which the receiver 

 fitted; and when it was filled with dry ashes the point was 

 thereby rendered sufficiently air-tight. It was supported by legs 

 so high that a spirit lamp could be placed under it, and any re- 

 quired temperature given to the air within. 



A second receiver of the same size was sometimes used for the 

 purpose of simultaneous comparison. The air within it was 

 cooled by inserting a tin canister filled with frigorific mixtures. 

 The thermometers were supported within the receivers, and thus 

 at the same time the same rays could be tested in the opposite 

 extremes of temperatures. 



I subjoin, as an example, the following table (p. 380) contain- 

 ing the results of an experiment made in February last, at eight 

 o'clock in the morning. It was a clear day and the sun shone 

 through a window into the room where the instruments were 

 placed. 



The first observation was the temperature of the room and in 

 the sun upon a mercurial thermometer. The lamp was placed 

 under the receiver, and as the temperature of the air was grad- 

 ually increased, the effect was noted until the heat in the sun had 

 attained the highest limit of the thermometer. The fourth col- 

 umn contains the differences between the thermometer in the 

 shade and the one in the sun. The fifth column shows the true 

 relative heat of the sun's rays at the different temperatures. It 

 was obtained as before explained by adding to the differences 

 the increase in the temperature of the air. Several observations 

 may be made in regard to the results in the table. 



