MEASUREMENT OF TEMPERATURE. 
187 
Details of Air Thermometer No. II. 
Volume of bulb V 0 = 77*01 cub. centims. 
Total volume of capillary tube='0840 cub. centim.; diameter, '03 centim. 
The U gauge tube was of very uniform bore : w=’0442 cub. centim. per centimetre. 
x=l, v 0 =T22 cc., /8 0 =5 = -001585, ^/ 0 = -0084~1 
0 H0 V ,j0 U' = 6>"=15°Cent. 
XZ=10, v= '520, I3=- 00675, ?/=-0133 J 
Mean coefficient of expansion of glass between 0° and 100° Cent., y— ‘0000251, by 
mercury weight thermometer. 
From the observations in ice and steam, on February 13, we have 
99 - 97 . 34-102 
12-620 
270-12. 
log ^=-89881. 
Po 
To find the other temperatures, @=~ P- 
For the platinum spiral the resistance of the connexions was, at 0° Cent., ’0139 : at 
353° Cent., "0221. The value of this small correction at intermediate temperatures 
was found by ruling a straight line on logarithm paper with sufficient accuracy. 
Applying corrections, we find R 0 =5"0845 B.A. ohms, colog R 0 =9"29375. 
As the U gauge tube had been made unnecessarily long, the ‘ q’ correction was 
large and negative. By direct comparison with the mercury of the manometer, the 
ratio of the density of acid to mercury at 15° was determined to be ‘1382 and 
the capillarity "45 centim. 
Thus, when x=0, q= — 3T2 centims. ; and, when cr=10, q——l'7b centim. 
From these details the “ correction diagram ” is constructed which is shown in 
Plate XI., fig. 5, for the purpose of illustrating the method of reducing the observa¬ 
tions. The ordinate scale, on one side, gives values of y, on the other, values of q, 
for the same abscissa scale of x. A difference of +5° in 6" makes y=-0132 instead 
of *0133 when «i=10, so that variations of 6" may almost be neglected. Only one 
line is therefore drawn, corresponding to 1 5° C. (The lines of the section paper 
are only indicated, every tenth line being reproduced in the diagram.) 
[When the apparatus was cooling the lower part of the bath was some 50° hotter 
than the upper. The platinum spiral was hung vertically in this instrument, and was 
deformed by its own weight, so as to be massed chiefly in the lower and hotter portion 
ot the bulb. The observations taken during cooling are, therefore, affected by a 
constant error amounting to two or three degrees, the mean temperature of the spiral 
being higher than that of the air.] 
2 b 2 
