BORE OF THERMOMETRIC TUBE 0’2 CM 
432 
Proceedings of the Royal Society 
Monday , 1st March 1880. 
Professor GEIKIE in the Chair. 
80 
The following Communications were 
read : — 
Fig. l. 
1. On Steam-Pressure Thermometers of 
Sulphurous Acid, Water, and Mer- 
cury. By Sir W. Thomson. 
The first annexed diagram represents a 
thermometer constructed to show absolute 
temperature realised for the case of water 
and vapour of water as thermometric sub- 
stance. The containing vessel consists of a 
tube with cylindric bulb like an ordinary 
thermometer ; but, unlike an ordinary ther- 
mometer, the tube is bent in the manner 
shown in the drawing. The tube may be of 
from 1 to 2 or 3 millims. bore, and the 
cylindrical part of the bulb of about ten 
times as much. The length of the cylindrical 
part of the bulb may be rather more than 
of the length of the straight part of the 
tube. The contents, water and vapour of 
water, are to be put in and the glass her- 
metically sealed to enclose them, with the 
utmost precautions to obtain pure water as 
thoroughly freed from air as possible, after 
better than the best manner of instrument 
makers in making cryophoruses and water 
hammers. The quantity of water left in at the 
sealing must be enough to fill the cylindrical 
part of the bulb and the horizontal branch of 
the tube. When in use the straight part of the 
