300 THEORY OF HEAT. [CHAP. IX. 



cients C, H, K, D denote the same specific properties as in the 

 preceding problems, and g is the half-side of the square formed by 

 a section of the prism. 



389. In order to make these results more intelligible by a 

 numerical application, we may suppose that the substance of which 

 the prism is formed is iron, and that the side 2g of the square is 

 the twenty-fifth part of a metre. 



We measured formerly, by our experiments, the values of H 

 and K ; those of C and D were already known. Taking the metre 

 as the unit of length, and the sexagesimal minute as the unit of 

 time, and employing the approximate values of H, K } C, D, we 

 shall determine the values of V and 6 corresponding to a given 

 distance. For the examination of the results which we have in view, 

 it is not necessary to know these coefficients with great precision. 



We see at first that if the distance x is about a metre and a 



half or two metres, the term -^- # 2 , which enters under the radical, 



Kg 



has a large value with reference to the second term - . The ratio 



of these terms increases as the distance increases. 



Thus the law of the highest temperatures becomes more and 

 more simple, according as the heat removes from the origin. To 

 determine the regular law which is established through the whole 

 extent of the bar, we must suppose the distance x to be very 

 great, and we find 



Kg 



390. We see by the second equation that the time which corre 

 sponds to the maximum of temperature increases proportionally 

 with the distance. Thus the velocity of the wave (if however we 

 may apply this expression to the movement in question) is constant, 

 or rather it more and more tends to become so, and preserves this 

 property in its movement to infinity from the origin of heat. 



