THE MECHANICAL EQUIVALENT OF HEAT. 
441 
value remained constant so long as the adjustment was unaltered. Any alteration 
in the fixing of the stirring shaft necessitated a re-determination of K. 
After experiment J 19, the whole apparatus was taken to pieces. It was then 
found that small fragments of gutta-percha had, by the continued impact of the 
water, been detached from the ring of gutta-percha which had been placed between 
the cooling tube and the tube down which it passed. Many of these fragments had 
collected beneath the base of the cylinder at and must have considerably impeded 
the flow of water. In consequence, therefore, before putting the apparatus together 
again, we removed all remaining gutta-percha surfaces which were exposed to the 
action of the water. The values obtained for K were, from this time, very different 
from preceding ones, and, once obtained, remained constant as long as the same mass ' 
of water was used. 
The experiments J 20 to 34, are in better agreement amongst themselves than the 
earlier ones, and the cause no doubt is that just indicated. 
The mean result of the earlier experiments is satisfactory as likewise the mean 
time of each experiment, but the times over small ranges (especially in experiments 
Nos. J 5 to 12) leave much to be desired. The fact that the quantity of heat 
developed by the stirrer was increased by the removal of the gutta-percha frag¬ 
ments is a proof that the flow of water was appreciably diminished by the 
obstruction. 
Section XII. —The Gain or Loss by Eadiation, &c. 
It has already been pointed out that the method of observation adopted enabled us 
to determine, with sufficient accuracy, the total loss or gain of heat per second at any 
temperature, apart from the supply due to current. We propose to use the phrase 
“ non-electrical supply ” to denote heat due to all other sources than the current. 
By the method described in Section XL, we were enabled to deduce the rise per 
second when the rate of revolution of the stirrer was 30, although the actual rate 
differed slightly from our standard one. The rate of rise, when radiation, &c., was 
eliminated, was first ascertained by noting the time of a small rise across the outside 
temperature. The temperature of the calorimeter was then gradually raised through 
the whole range by means of stirring only, and the times ascertained of small changes 
at the different temperatures. Assuming the “stirring heat ” to be the same at all 
temperatures (when the rate is the same), we can deduce the radiation coefficient. 
(By radiation coefficient we denote the loss or gain in temperature per second, due to 
the combined effects of radiation, conduction, and convection, for a diiference in 
temperature of 1° C). 
One advantage of this method is, that all observations of temperature are taken on 
MDCCCXCTII.-—A. 
* Plate 2, fig. 2. 
3 L 
