THE MECHANICAL EQUIVALENT OF HEAT. 475 
1 
Observations on Tables XXXV. and XXXVI. 
Experiments 1 to 4. 
These have been rejected and the observations are not included in the Tables. 
The discrepancies over the shorter ranges are absurdly great, and the mean times 
far too large. During these experiments we had great difficulty in maintaining the 
potential-balance; this ought to have been sufficient to indicate the source of error, 
but, at the time, we attributed it to want of practice in the observers. 
It must be borne in mind that it was not until many weeks after the close of our 
observations that the reductions were completed, so that, at the time of experimenting, 
we were wholly in the dark as to the actual value of our results. Our only means of 
obtaining any glimpse of the value of a particular experiment was its resemblance to 
some other one taken under similar conditions, but, as all the conditions were never 
precisely the same, we could thus obtain little information. 
We have now no hesitation in assigning the following cause to the failure of these 
four experiments. With this weight of water, the depth in the calorimeter, when 
the stirrer was at rest, was only 2 centims., and as, when rapid stirring took place, a 
great portion of the contents must have been within the cylinder and in the upper 
portion of the calorimeter, it is evident that the higher parts of the coil must have 
been at times uncovered, since it required 1’5 centims. for complete immersion. This 
would account (1) for the irregular behaviour of the potential-balance, and (2) for the 
great lengthening of the times shown in these experiments. We at no time antici¬ 
pated success with so small a mass of water, but the excellent results obtained from 
our stirring experiments on this weight (see Table XXI.) justified the attempt. 
Experiments 5 12. {Group B.) 
These experiments are only slightly more satisfactory than those we have rejected. 
The cause is partly that so frequently alluded to in Section XII., viz., obstructions in 
the openings at the base of the internal cylinder, the resulting irregularities in the 
throw of the stirrer affecting not only the non-electrical supply, but also changing the 
coefficient of increase in the resistance of the wire. That this is the case is indicated 
I by the results of Experiment 9, where the E.M.F. was so reduced that the current 
was only •! ampere, and the changes in the temperature of the wire were less marked. 
This experiment was performed in order to test the accuracy of our various corrections, 
rather than as a serious effort to determine the value of J. The observations in this 
experiment only extended over f of our total range, for, had we endeavoured to carry 
it out through the upper ranges, its duration would have extended over some hours. 
In every case (excepting as above stated. Experiments 1 to 4) we have given all 
the numbers recorded, because, however bad individual observations may appear, we 
have no sufficient grounds for their rejection. The omissions in the table represent 
experimental mistakes; in No. 5, E-ange 7, the storage circuit was broken foi a second 
3 P 2 
