256 Professors W.E. Ayrton and J. Perry on 



of September 1876, on the same stone ball of 6*9 (six and 

 nine tenths) centims. radius, and found that the fourth method, 

 applied to the curve of falling temperature between 1050 

 seconds* and 2100 seconds, gave 



K = 0-00578, 



E = 0-00263. 



We did not use the earlier part of the curve, as we were de- 

 sirous that all terms except the first should disappear in the 

 calculations. The portion after 2100 seconds we also did not 

 employ, as it is more difficult then to judge between what 

 isothermals lies the curve obtained from the experiments. 



In the early part of September, 1876, we obtained the curve 

 D D D, fig. 4, for the cooling of the centre of a stone ball of 5*5 

 (five and a half) centims. radius, initially heated to 73°*62 C, 

 represented by O A, the temperature of the stream of water 

 outside when plotted giving the curve dddj the scale of time 

 in both curves being such that X represents 50 minutes. 

 From these two curves, using the fourth method, we found that 



K = 0-00548, 



E = 0-00495; 



on the assumption that the curve is within the exisothermal 

 for 21°*5 C. at 450 seconds, and within the exisothermal for 

 20°"2 C. at 1200 seconds. In the above calculations, although 

 there is reason for believing that the stone, while of the same 

 general character, differs somewhat in the two balls, we were 

 compelled to use in both cases the same value of the specific 

 heat (0*5738) per unit volume obtained experimentally from 

 some fragments of the stone remaining after the turning. Our 

 results obtained by the fourth method are therefore: — 



Kadi us of ball, 

 in centimetres. 



Initial tempera * 



ture, in degrees 



Centigrade. 



Outside tempe- 

 rature at 2700 

 seconds. 



K. 



E. 



69 

 6-9 

 5-5 



6962 

 69-25 

 73-62 



o 

 164 

 17 75 

 J 7-9 



000590 

 00573 

 000548 



000252 

 000263 

 0-00495 



As we have only drawn attention to four curves obtained 

 from the experiments, one in § V. and three in § VII., it may 

 be as well to mention that several other curves were drawn 

 from sets of observations made during July, August, and Sep- 

 tember in the earlier part of the* investigation. As, however, 



