ON THE MECHANICAL EQUIVALENT OF HEAT. 
317 
The first provision made for measuring the temperature of the entering water was 
an opening in the bend of the pipe over the inlet valve, with a 
vertical |-inch brass tube soldered in, about 4 inches long. This 
admitted of an indiarubber cork, through the centre of which a 
thermometer was passed into the pipe, as shown in fig, 5. This was 
afterward replaced by a glass thermometer chamber, as shown in the 
figure, Plate 5. 
To measure the temperature of the water leaving the brake it was 
necessary, by means of a pipe fixed to the mouth of the outlet valve, 
to bring the effluent water above the balancing lever of the brake, 
and to one side of it. This pipe was arranged so as to admit the 
introduction of a vertical thermometer into the ascending pipe, much 
in the same way as the other. In the first instance the extension 
passage and the thermometer were all rigidly attached to the brake, and moved 
with it, which entailed a re-balance of the brake. Subsequently another arrange¬ 
ment was made. The thermometers used were divided to one-fifth of a degree 
Fahrenheit ; they were both immersed in the flowing water to within a few degrees of 
the top of the mercury. They were compared at equal temperature, but otherwise 
subjected to no tests for accuracy of scale. 
In making the experiments the link connecting the inlet valve with the automatic 
gear was removed and the valve was set open, the supply being adjusted by the hand- 
cock below. The head on the inlet being constant, when the cock was set the flow 
was practically steady. The quantity of water in the brake then depended on the 
outlet valve, which, with the exception of a little trouble at starting and stopping, 
soon overcome, kept the brake lever steady. 
To catch the water after leaving the outflow thermometer, the extension pipe 
turned horizontally over the lever and then turned downwards into a basin, the lip 
of which was above the mouth of the pipe, and from the basin flowed in a short 
trough, from which it was caught in buckets. In these it was taken to the scales 
and carefully weighed. This was a primitive arrangement, and required several 
assistants, but was found capable of considerable accuracy up to about 40 lbs. a 
minute. 
In making these experiments the engines were kept running at nearly constant 
speed by keeping constant pressure in the boiler. The speed being indicated on 
the speed gauge as well as recorded on the counter. 
The water entering the brake, coming, as it did, from the town’s main, was at 
nearly constant temperature between 40° and 50° Fahr., according to the time of the 
year, and varying less than a degree throughout several trials. 
The rise of temperature was adjusted by the quantity of water admitted, according 
to the work, so that the final temperatures as well as the initial were as nearly as 
possible the same in the different trials. 
