ON THE MECHANICAL EQUIVALENT OF HEAT. 
409 
VI.—Corrections due to the Fall in Pressure between the Supply and Discharge Pipes. 
62. From observations taken on October 1st, 1896, I determined the pressure on 
the thermometer in the supjdy pipe to be ;— 
In the 1200 ft.-lb. trials.15 inches of mercury. 
,, 600 „ ,, .... 11 ,, ,, 
,, 400 „ ,, .... 97 ,, „ 
I have already stated that the pressure on the thermometer in the discharge pipe 
was 11’3 feet of water in all trials. 
From these varying pressures two corrections are obtained as follows :— 
(a.) Elevation of Temperature Readings by the Pressure on the 'rhermometers. 
1200 ft.-lbs. 
600 ft.-lbs. 
400 ft.-lbs. 
Pressure on thermometer bulb 
in supply pipe in inches of 
mercury 
15-0 
11-0 
9-7 
Consequent elevation in readings of 
temperature (0°-0072 per inch) 
0°-108 
0'’-0792 
0°-0698 
Pressure in discharge pipe in feet 
of -water 
11-3 
11-3 
11-3 
Consequent elevation in readings of 
discharge temperature (0°-0066 
per inch of mercury) 
0°-066 
0“-066 
0°-066 
Percentage correction to heat 
0-042 
0-013 
0-004 
obtained 
1-8 
1-8 
1-8 
= 0 0233 
= 0-0072 
= 0-0022 
If we now confine our attention to the combination of 1200 and 600 ft.-lb. trials, 
the relative correction to the difference of heat is 
0-000233 - t X 0-000072 
1 . 
2 
0-000394, 
i.e., the correction factor to K on this account is 
(1 - 0-000394). 
Considering next the 1200-400 ft.-lb. determinations, the relative correction to 
the difference of heat is 
0-000233 - i X 0-000022 
3 
0-000339, 
3 G 
VOL. CXC.—A. 
