S2 Mr, Emmet t on the Feb. 



same as that of the surrounding calorific medium ; for if it be 

 greater, caloric will flow from the body into the surr6unding 

 medium ; if less, to it ; consecj[uently, when a mass of matter is 

 placed in a heated medium, it will continue to absorb caloric 

 until the sensible elasticity of its calorific atmosphere is precisely 

 equal to that of the surrounding caloric ; under which circum- 

 stances both the body and the medium will have an equal effect 

 upon the thermometer. The elasticity then of the caloric only 

 can have any effect upon the thermometer ; for whatever be the 



Suantity absorbed by the body, the thermometer will experience 

 le same degree of elevation, whether appUed to the medium, or 

 to the body itself. 



Let now the mass of matter thus heated be brought into a 

 medium of lower temperature : it is now evident, prop. 6, cor. 

 and prop. 11, that the sensible elastic force of the calorific atmo- 

 sphere will exceed that of the surrounding medium ; the caloric 

 will, therefore, have a tendency to diffuse itself: there are three 

 different circumstances under which this may take place. 



Case 1. — Suppose a warm solid to be brought into a medium 

 of absolute cola, in vacuo, and entirely beyond the attracting 

 force of any other form of matter ; one force, viz. the elastic 

 force of the surrounding caloric being removed, the calorific 

 atmosphere of the body will have a tendency to enlarge its 

 dimensions ; and since the density of the several concentric 

 strata is uniform, it must move in right lines, which meet in the 

 centre of the body (supposed spherical), which radiation of heat 

 will continue until the density of the lower strata is so far 

 reduced as only just to balance the pressure of the superior rare 

 ones, when the atmosphere becomes quiescent in all its parts ; 

 in this case, therefore, the radiation of caloric arises entirely 

 from the motion into which the calorific atmosphere is put by 

 the removal of the elastic force of the surrounding caloric. The 

 caloric cannot leave the body, since there is no other form of 

 jnatter by which it can be attracted. 



Case 2. — Suppose, that instead of being placed in absolute 

 cold, the warm mass of matter is brought into a medium having 

 a lower temperature than that to which the body was exposed ; 

 ;the other circumstances remainin^j, the calorific atmosphere will 

 dilate itself, its parts moving in right lines, which will continue 

 until the diminished density of the lower strata balances the 

 elasticity of the surrounding caloric, and the pressure of its own 

 superior strata, when the radiation ceases. In both these cases, 

 the quantity of caloric contained in the atmosphere of the body 

 is precisely the same ; viz. that which it had at its highest tern* 

 perature. 



Case 3. — Suppose, in addition to either of the other cases, that 

 masses of matter are placed within the calorific atmosphere, 

 having a lower temperature than the parts of the atmosphere in 

 which they are placed. The calorific atmosphere will have a 



