1888.] J. T. Bottomley on a Practical Air Thermometer. 87 
For all these objects I find it most convenient to construct separ- 
ately the manometric columns, and the air reservoir with its volume 
indicator; connecting these two parts of the instrument only by 
flexible tubing. This arrangement necessitates an apparatus for 
regulating the pressure under which the air in the thermometer is 
maintained. 
The complete instrument is shown in fig. 1. A is the air 
reservoir and volume indicator, B is the manometric gauge, and C is 
the pressure apparatus. 
The air reservoir and volume indicator I shall call for brevity the 
volume gauge. It is made in two forms (figs. 2 and 3) — the 
form shown in fig. 2 for the lower, and the other for the higher 
temperatures. The bulb a, which is generally either globular or 
cyhndrical, is connected by a very fine capillary tube e with a some- 
what wider tube d. At &, V there are two cylindrical bulbs of the 
same size. The tubes dd and d'd' are of precisely the same diameter, 
being cut from the same length of uniform glass tubing. The 
