1894.] entitled " The Mechanical Equivalent of Heat." 25 



as the difference, which would diminish our temperature range by 

 about 1 in 3000, and would increase the value of J by a proportionate 

 amount, although it would not affect the temperature coefficients of 

 the capacity for heat of water or the specific heat of the calorimeter. 

 I do not, however, feel that this point is sufficiently established to 

 make it advisable to apply the correction to the previously published 

 results. 



Section II. 



I regret to state that we have discovered a serious error in the 

 arithmetic. 



On pp. 407 410 is given an account of the comparison of the coils 

 in the resistance-box with the B.A. standards, and Table XI gives in 

 full the numbers actually obtained during the comparison. In order 

 to simplify our work we constructed a table for our own use which 

 gave the value of each coil in terms of a legal ohm, and afterwards 

 transferred them (see p. 410) into true ohms. Unfortunately the 

 10-ohm coil in the bridge arm was entered in this private table as 

 10-0077, whereas it ought to have been 9'9977 an error of 1 in 1000, 

 having its origin in a mistake in addition. The experimental numbers 

 actually given in Table XI will show that the ratio of the bridge 

 arms was 9'9734/997'87, that is, 0*0099947, or, if expressed in legal 

 ohms, 9-9977/1000-30 instead of lQ-0077/1000'30, as given on line 13, 

 p. 410. 



The mistake is obvious to anyone who compares the numbers given 

 in Table XI with the conclusion drawn on p. 410. The whole of the 

 arithmetic was carefully revised by both Mr. Clark and myself, but 

 an error of this kind in simple addition is precisely the one to escape 

 observation. The annoying circumstance is that a similar mistake in 

 any of the other coils would have had no appreciable effect on our 

 conclusions, but occurring as it did in the ratio of the bridge arms 

 it affects all succeeding tables. 



I would venture to add that this incident shows how advisable it 

 is, in work of this kind, to give in full all the experimental numbers 

 on which the conclusions are based. 



In consequence of this discovery I have carefully again revised 

 nearly the whole of the calculations, but I am glad to say that with 

 the exception of two or three obvious misprints I am unable to detect 

 any further arithmetical mistakes. 



The effect of the correction thus rendered necessary is to decrease 

 the value of R, in all the tables where the reduction to true ohms is 

 given, by 1 in 1000 ; hence the value of T in Tables XXXVII, XL, 

 XLI must be increased in the same proportion. The resulting cor- 

 rection is a simple one, for, as the value of J varies directly as T, it 

 has only to be increased by 1 in 1000. Fortunately the temperatures 



