THE MECHANICAL EQUIVALENT OF HEAT. 
Oij o 
Date. 
Readings obtained from thermometer PI when immersed 
in steam at temperature 
Correction used 
in experimenis. 
212 ° 
213°-8 
215°-6 
28 Nov., 1895 
211-43 
213-26 
215-01 
+ 0-57 
4 Dec., 1895 
211-44 
213-28 
215-03 
+ 0-56 
5 Dec., 1895 
211-5 
213-33 
215-07 
+ 0-5 
6 Dec., 1895 
211-51 (rising) 
• • 
• « 
1 j_ 0'4-fi 
211-53 (falling-) 
• • 
• « 
12 Dec., 1895 
At tempera 
ture 21U°-46 reading 
was 210°-05 
9 Jan., 1896 
213-38 (rising) 
[ 1 C\-A A 
213-40 (falling) 
> -j- U tkTi 
17 Jan., 1896 
* , 
213-49 
, , 
+ 0-34 
2.3 Jan., 1896 
213-49 
+ 0-34 
31 Jan., 1896 
213-49 
+ 0-34 
8 Feb., 1896 
211-76 
213-57 
215-3 
+ 0-24 
20 Feb., 1896 
211-78 
213-6 
215-34 
+ 0-22 
At 
211°-.34 reading was 
211°-1 
16 Mar., 1896 
211-86 
213-66 
215-4 
+ 0-14 
At 
211°-07 reading was 
210°-87 
18 April, 1896 
, , 
213-7 
215-45 
+ 0-11 
15 June, 1896 
211-94 
213-74 
215-5 
. + 0-06 
6 July, 1896 
211-96 
213-75 
215-52 
+ 0-04 
25. In the case of each of these thermometers, viz., Q2 and Pi, the water 
surrounding them was under a very considerable pressure, and it was therefore 
necessary to determine the effect of pressure on the reading given by each, 
A piece of strong glass tube, fig. 9, about 1 foot in length and f inch inside 
dia.meter, having one end fused up, was provided with a slightly wider mouth, in wdiich 
was inserted a small branch pipe, A. This branch again split up into two arms, one of 
which, B, was connected through a rubber tube with an air receiver in which the 
pressure was indicated by a U-gauge, while the other, C, communicated directly with 
the atmosphere. Each of the branches B and C could be closed at will by means of 
a screw clip on the rubber tubing. 
The pressure tube having been about half filled with water, the thermometer under 
consideration was fixed inside it by means of a cork, D. 
In the case of the freezing-point thermometer, Q2, the pressure tube was then 
surrounded with pounded ice. After the contained water had cooled sufficiently for 
the thermometer inside to remain steady, the communication with the atmosphere 
was closed, and the full pressure of the air receiver put on the thermometer bulb by 
opening the clip on the tube, B. The rise in the reading due to the known rise of 
pressure was then noted. A. number of these observations were made, using different 
additional pressure in each case. The result obtained was that for a rise in pressure 
on the bulb due to 1 inch of mercury, the rise in the reading wms 0'0072°. 
In the case of the boiling-point thermometer, Pi, the pressure tube was immersed 
VOL. CXC.—A. 3 D 
