170 



Mr. E. Foote on the Heat in the Sun's Rays. 



1st. That the heat in the sun's rays is not uniform, such as 

 would proceed from a great heated body of uniform intensity, 

 nor is it such as was received from the canister when kept at the 

 same degree of heat, but that it varies and is dependent upon 

 the temperature of the air. 



2ndly. That the effects of the sun's rays upon the thermometer 

 at the diflFerent degrees of heat in the receiver is the same that 

 has usually been observed at similar temperatures in the open 

 air. It is easy, by changing the heat within the receiver, to 

 imitate the power of the sun's rays that has been observed at any 

 time or in any place; indeed at the same time the same rays 

 may have in one receiver the burning heat of a summer's sun, 

 and in the other only the feeble action of winter. 



3rdly. It appears that heat does not travel along with the rays 

 of light, as has been usually supposed, but that it is received, or 

 parted with, lost or acquired, according to the temperature of the 

 place that the rays illuminate. The same rays that within the 

 receiver have the high intensity belonging to summer, on passing 

 to the outside are reduced again to a winter's temperature. 



In view of these results, it seems to me to accord better with 

 the facts to attribute to the sun's rays, perhaps to all light, an 

 action of some kind on such heat as they come in contact with, 

 producing thereby the effects that we have been accustomed to 

 attribute to an enormous temperature in the sun. Each planet 

 may be supposed to possess its own atmosphere of heat : this 

 will be affected by the sun's light as the heat within the I'eceiver 

 was affected ; but they need not be frozen by their great distance, 

 nor burned by their near approach to the great luminary. 



It becomes an interesting and important inquiry to ascertain 

 the circumstances that affect the action of light on heat. 



One of the most obvious is, that the amount of action depends 

 upon the quantity of light. The clearness of the atmosphere 



