5ARUS-1 
PORCELAIN AIR THERMOMETRY. 
213 
?o long that the position of the thread may be seen. This furnishes r 
If equation ((>). It is frequently convenient to make this measurement 
or unequal heights of the columns of mercury in the two arms of the 
nanometer. In this case i?, of course, is the effective tension of the gas. 
The difference in height of the menisci is read off by the cathetometer. 1 
Volumetry of bulb. — Equatious (4) and (5) contain the quantity V, 
>r the volume of the bulb of the air thermometer at zero centigrade. 
This may, of course, be measured directly, before the high temperature 
work, by calibrating with water. If, however, a bulb non-glazed in- 
ternally be used it is exceedingly difficult to dry it again thoroughly. 
Hence I have applied the volumetric method already utilized above in 
the case of stems. In the case of a manometer like the one described 
in Fig. 40 this method is applicable with great elegance, inasmuch as 
pressure can be varied over a large range and volumes read off with 
facility. In the following table an example of data obtained in this 
way is given. i\ and p are corresponding values of the volume of 
the gas in the manometer tube B G (Fig. 40), and of the pressure. 
Measurements are made with the bulb and manometer in the air, and 
no thermal correction is applied : 
Table 56. — Volumetry of hull. 
Date. 
Vl 
P 
Vo 
cc. 
cm. 
cc. 
Oct. 14 
4.9 
75.88 
279. 6 
122.2 
53.73 
4.8 
75. 93 
280.1 
122.2 
53.77 
Oct. 15 
3.0 
75.65 
281.0 
120.2 
53. 55 
30.0 
75. 66 
280.9 
120. 2 
53. 59 
9.7 
73.97 
282.0 
120.8 
53.56 
6.5 
74.82 
281.3 
120.8 
53. 55 
4.9 
75. 46 
281.4 
120.9 
53. 70 
7.4 
74. 93 
279. 9 
126. 6 
52. 96 
Oct. 16 
4.0 
* 75. 24 
280.1 
126.0 
52. 64 
4.0 
75. 22 
281.3 
120.5 
53. 41 
3.0 
75. 5 1 
279. 9 
120.5 
53.38 
3.0 
75.53 
Mean v 
281.3 
8 = 280.73 
1 Many operations may be simplified by using Landolt and Boernstein's physical 
tables ; Berlin, 1883 ; cf. pp. 5 to 7. 
(867 
