I ;5 Reflections on Heat. 



One of the two bulbs is protected from the influence 

 (calorific or frigorific) of the warm or cold bodies pre- 

 sented to the other bulb by means of light screens cov- 

 ered with gilt paper; when the air in this latter bulb is 

 warmed or cooled by a body warmer or colder than the 

 thermoscope to which it is thus presented, the elasticity 

 of the air is affected by this change of temperature, and 

 the little bubble or column of spirit of wine which is in 

 the horizontal portion of the tube is compelled to move 

 and to take a new position. 



The direction of the motion of this bubble indicates 

 the nature of the change which has taken place in the 

 temperature of the air which is enclosed in the bulb to 

 which the body is presented, and the distance traversed 

 by the bubble is the measure of the increase or diminu- 

 tion of the elasticity, and, as a consequence, of the tem- 

 perature of that air. 



If the bubble recedes from the bulb to which the 

 object experimented upon is presented, it is evident 

 that the air enclosed in the bulb has been heated by the 

 influence of this body ; but when the bubble of spirit 

 of wine advances towards this bulb, we have a proof 

 that the air in the bulb has been cooled. 



The rapidity with which the bulb moves is propor- 

 tional to the intensity of the action of the object pre- 

 sented to the instrument. 



In order to compare the intensity of the calorific or 

 frigorific actions of two different objects, they are pre- 

 sented at the same time to the two bulbs of the instru- 

 ment, and their respective distances from the bulbs so 

 regulated that the bubble of spirit of wine remains at 

 rest in its proper position. 



In this case it is evident that the action of the two 



