ON HtAt ANtf LlGtiti 159 



bodies we fubjedt to experiment are constantly furroundeo! oft 

 all fides by the air and other bodies which act on air inftruments 

 continually, and often in a very perceptible manner; and we 

 can never hope to ifolate a cylinder fo completely that the ap- 

 parent progrefs of heat in its interior (hall perceptibly obey the 

 law we have juft difcovered. In common cafes it deviates wide- 

 ly from this law. 



As the caufes of this deviation are well known, we will fee Appreciation of 

 whether there be no means of appreciating their effects.. 



The furface of the cylinder being furrounded by the atmof- The atmofphere 

 pheric air and other bodies, all which are of a known and fen- cylinder, 

 fibly conftant temperature, we may determine the comparative 

 effects of thefe bodies on the different parts of the furface of 

 the cylinder. 



In thofe parts of the cylinder which are hotter than the air by cooling 



and other furrounding bodies, the furface of the cylinder will ! ts h . ot P art a * d 

 » ".""" ', J heating its cold 



be cooled by the action of thefe bodies ; but if one of the ex- part, 



tremitics of the cylinder be colder than the atmofpheric air, 

 thofe parts of the cylinder which are colder than the circum- 

 ambient fluid will be heatedby its influence and that of the fur- 

 rounding bodies. 



We will begin with examining the cafe where the coldeft If . one extre- ^ 

 extremity of the cylinder is at the fame temperature as the fur- be' at ^he tern- 1 

 rounding air. Let us fuppofe then, that the experiment with perature of the 

 boiling water at the one end and freezing at the other be made hotter E ^^ 

 when the temperature of the air is at the freezing point, or 32° 

 of Fahrenheit. 



In this cafe it is evident that the furface of the cylinder mull the furface 



every where be cooled by the influence of the furrounding at- Wl '' beever y 

 mofphere. The queftion then is to determine the comparative 

 effects, or the relative quantities of refrigeration or lofs of heat, 

 that mutt take place in the different parts of the cylinder: and in 

 the firft place it is clear, that the hotter a given part of the cy- 

 linder is, the more heat it muft lofe in a given time, by the in- 

 fluence of the furrounding cold bodies; whence we may con-, —but moil fo 

 elude, that the refrigeration of the furface of the cylinder by wheic the k e * : 

 the influence of the air and other furrounding cold bodies muft ** ^* 

 necetfarily diminith from the extremity of lh& cylinder A, which 

 is in contact with the hot water, to its extremity E, which is 

 io contact with the cold, 



From 



