524 Proceedings of the Royal Society of Edinburgh. [Sess. 
either with the atmosphere, with a vacuum reservoir and water pump, or 
with a pressure reservoir and pump. 
The manipulation may be understood from an example. When the 
vapour pressures of water below one atmosphere were being measured, the 
temperature of the bath was first brought to the desired point. The exit 
to the vacuum bottle and pump was opened, and the pressure in the iron 
bottle was reduced until the water in the bulb boiled. This exit was then 
closed. When the air and dissolved gases had been expelled, the stopcock 
leading to the atmosphere was opened. Simultaneously, the rubber tube 
attached to this stopcock was grasped with the fingers at two places, and air 
was admitted in small portions until the levels of the water in the U-tube 
were identical. The stopcocks on the exit of the atmosphere, as well as that 
on the gauge, were then closed, the gauge was read, and the temperature 
reading was confirmed. The whole process of boiling out and adjusting was 
then repeated, to make sure that all gases had been expelled from the 
