374 
DR. J. P. JOULE ON A NEW DETERMINATION 
In making an experiment for the equivalent the weight of the calorimeter filled 
with distilled water was first carefully ascertained. It was then screwed on to the 
axis, and the fine silk cords attached to the scales, k k, fig. 1, were adjusted. 
Thermometer A was then introduced into one of the tubulures, and after sufficient 
agitation of the water by means of the paddle itself, its indication was observed 
through a telescope. The thermometer was then removed and a caoutchouc stopper 
placed in the tubulure. The axle was then brought rapidly up to the velocity which 
produced friction sufficient to raise the weights about a foot from the ground. My 
son, Mr. B. A. Joule, who turned the wheel, could, by observing the position of the 
scales in a mirror, keep them very steadily at a constant height during the whole time 
of revolution. The wheel having been rapidly brought to a standstill, the temperature 
of the calorimeter was again ascertained. 
In the experiments in Table I. the number of revolutions of the axis when the weights 
were off the ground was added to half the number occupied in the acts of starting from 
rest and returning to rest. 
© 
Previously to, and subsequently to, every such experiment others were made under 
similar conditions as to the observation of temperatures, &c., in order to ascertain the 
effect of the atmosphere on the temperature of the calorimeter. The indications of 
the thermometer for temperature of air are always reduced to the graduation of 
thermometer A. 
Experience had already shown me that the thermal effect of the air on the calori- 
meter was not exactly proportional to the difference of their temperatures. This 
might arise from variations in the radiating powers of brass and glass from day to 
day. By making experiments for the air-effect immediately before and after one for 
the equivalent, I sought to neutralize any error arising from this circumstance. The 
last column but one of the first part of the following Tables gives the amount of 
correction required to be applied to the temperature of the air so as to make the 
effect proportional to the difference of temperatures. The figures in the last two 
columns are then used for calculating the corrected rise of temperature in the last 
column but one of Part 2 of the Tables. 
