964 ^^ '^^^ NATURE OF HEAT. 



vibration of rays, it merely causes them to converge, collects 

 and unites their effect. The intensity of vibration in th« 

 focus of the mirror is not greater than that of each of the 

 rays before they converged ; but as the force of all the rays 

 is concentrated in the focus, the heating etiect will be greater 

 there; that is, a body in the focus will be heated much 

 sooner than by the operation of a single ray, but will never 

 attain to an intensity of vibration arreater than that of a single 

 ray. In like manner, althoui^h the force of rays of sound be 

 accumulated in the focus of an elliptical chamber, yet the 

 note, or pitch of the sound, i. e. its intensity of vibration, 

 remains the same. 



Now vibrations of a certain intensity occasion the sensa*^ 

 tion and phenomena of cold ; the accumulation of rays of 

 vibration of this intensity by means of a concave mirror, as 

 before, does not alter their intensity, but merely converges 

 and collects their force, and thus increases the effect of pro- 

 ducing co'd ; and this it does, to the very same extent, pro- 

 vided all circumstances be equal, as the effect of producing 

 Experiment, beat was increased by converging the rays of heat. I have 

 endeavoured to ascertain this by experiment. The tempera- 

 ture of the atmosphere was 60*. Two mirrors were properly 

 opposed to each other ; in the focus of one was placed a ther- 

 mometer, in that of the other a cubical canister, one side of 

 which, (namely, that opposed to the mirror), was blackened. 

 The canister was now filled with water at 90°. The effect 

 on the thermometer in time and extent was marked: the 

 canister was then removed, and its place supplied by a similar 

 one containing A saline solution at 30*. The eff*ect on the 

 thermometer was opposite, but equal in time and in degree, 

 to that of the former experiment. 



This fact is of an importance not to be easily appreciated; 

 it appears to me to identify heat with vibration. 



Effects of Heat. 



H^tQUofheat, In the former part of my paper I have related some facts, 

 which are not only inexplicable on the theory of repulsive 

 caloric, but which appear to afford some degree of contra- 

 diction to it J it will therefore appear, that an explanation 



of 



