380 
PROFESSOR 0. REYNOLDS AND MR. W. H. MOORBY 
To find T, the temperature at which the scale gives correct readings, we have, if 
T = ^ 4- 32°, 
1 + ^ X 0-000012 _ 30 
1 + 35 X 0-000012 30-000138 ’ 
which gives t = 31° and T = 63° Fahr. 
The coefEcient of expansion of the mercury column relative to the brass scale is 
0-000088. 
Now if Ht = reading of barometer in inches at T° Fahr., and as before 
t=T - 
then the corresponding corrected height of the column at a temperature of 63° Fahr. 
1 + 31 X 0-000088 
1 + X 0-000088 ^ 
1-002728 
1 + ^ X 0-000088 
H 
Tj 
and if Hq = the corresponding pressure reduced to inches at the freezing-point, then 
H63= Ho(l + 0-0031). 
Therefore for any recpiired pressure Hq inches at a temperature of 32° Fahr., the 
corresponding reading at T° Fahr. is 
H 
T 
1 + 0-000088^ 
1-002728 
Ho X 1-0031, 
or, allowing for the capillarity depression in a half-inch tube, this becomes 
Ht = (1-00037 + 0-000088^) Hy - 0-009. 
This formula has been used throughout to determine the steam pressures required 
for the verification of boiling-points to be discussed later (pars. 23 and 24). 
The Thermometers. 
21. The thermometers used for the measurement of the temperatures of siqDply 
and discharge of the stream of water passing through the brake were supplied by 
Mr. J. Casartelli of Manchester. 
Their indications were read through the glass walls of their respective chambers 
by eye simply, parallax l^eing avoided by the use of a small mirror placed behind 
the thermometer in each case. 
