THE LAWS OF CONDUCTION OF HEAT IN BARS. 



97 



§ IV. — The " Statical Curve of Cooling" Becapitulation and Application of the Method 



of Deducing the Conductivity. 



96. It will be convenient here to recapitulate, from Arts. 5, &c. of the former 

 part of this paper, the use which is to be made of the data obtained from the two 

 fundamental experiments described in the previous sections, namely, the deter- 

 mination of the Curve of Statical Temperatures (Table II. Art. 61), and the rate 

 or velocity of Cooling of the bar at any temperature (Table VII. Art. 89). 



97. Let A B be the bar, kept hot at the extremity A, and left to assume a per- 



manent temperature at its various points under natural causes. Let the upper 

 curve, or DFE, represent by its ordinates (as FC) these temperatures. All the 

 heat that enters the bar at A, and is propagated along it, has to be accounted for. 

 Since the bar is so long that at the end B the heat has become insensible, the 

 entire heat entering the bar at A has been dissipated from its surface in various 

 proportions, according to its temperature, between the point A and some remote 

 point E where the elevation of temperature is practically insensible. In like 

 manner, if we take any point C in the bar, the heat transmitted from the hotter 

 end, by conduction across the transverse section of the bar at C, is dissipated 

 by the cooling of the bar between C and E. To know the quantity of heat 

 passing across this transverse section, we have therefore to ascertain the aggre- 

 gate loss of heat from the surface of the bar to the right hand of C. 



98. To do this, we must construct what I call the Statical Curve of Cooling, 

 which is represented in the same figure by the curve LHM, beneath the bar AB. 

 The ordinate C'H represents the heat lost by the bar per minute, from the portion 

 CC, whose temperature is represented by CF in the upper curve. This loss or C'H, 

 is found from Table VII., by entering it with the thermometer reading CF, which 

 again is known from Table II. in terms of the position of the point C in the length 

 of the bar. Thus all the ordinates of the Statical Curve of Cooling, LHM, can 



VOL. XXIV. PAET I. 2D 



