THE MECHANICAL EQUIVALENT OF HEAT. 
479 
The experiments on the heat developed by the stirrer give ns the values of 
(See Table XXVII.) 
1. The first step in the calculation of our observations has been to correct, where 
necessary, all times for the clock error, which was + ‘0004125, up to J 9 inclusive. 
This correction has been applied in Table XXXYIII. 
2. We found the value of cWJdt, i.e., the rise per second jn’oduced by the combined 
effect of aU sources of gain or loss (Table XXXVII., col. 4). 
3. Since the rate of revolution throughout an experiment was always nearly 30 per 
second, Ave eliminated irregularities in the rate by reducing to rate 30 by means of 
the formula given in (6). Thus we obtained the value cW^lclt would have had, had 
the rate been uniformly 30 per second. This reduction is shown in Table XXXVII., 
cols. 5 and 6. 
4. In order to be able to more readily compare experiments performed under 
almost identical circumstances, the next correction applied was that for the tem¬ 
perature of the Clark cells. Lord Rayleigh gives the formula 
Ejg = E^-|l + *00077 {t - 15)} 
hence 
E^,. = Wt {1 + ’00154 {t - 15)}.(11), 
where t is the temperature of the Clark cells. 
This correction cannot be applied to dB-^jdt as a whole (equation 9) but only to the 
portion [dOJdt)^ the electrical supply. the correction was always very small, it 
was sufficient to find the approximate value of {ddijdt)^ by subtracting, at any 
temperature, the value of {dO^fdt)^ as given in Table XXVII., and then find the 
correction on the value of {dOjdt)^ so obtained by formula (ll). The result of this 
correction gives col. 7, Table XXXVII. 
The correction wms applied in this order as we could thus compare all the experi¬ 
ments performed Avith the same E.M.F.’s so long as the values of cr and p Avere the 
same. The results at this stage of their reduction are given in Tables XXXVIII. 
and XXXIX. 
5. Table XXXVII., col. 8, gives the Amlue of {d6jdt)Q taken from Table XXVII. 
This subtracted from col. 7 gives the value of [ddjdt)^, i.e., the rise per second due 
to the current only, the difference of potential at the ends of the coil being n Clark 
cells (col. 9). 
Hence equation (8) is reduced to 
