Maker's Name: 
W. Edwards & Co. Ltd., London
Where made: 

A vacuum gauge where a sample of gas is compressed by a known ratio to be measured by a mercury manometer.

Lacquered wooden upright stand supporting vacuum tubes and compression bulb. Mounted below the assembly, a moveable metal weight, acting as a plunger. The McLeod gauge is a form of mercury manometer adapted for the measurement of pressures in the 1 - 10-3 Torr range.

To make a pressure measurement, the weight is lowered emptying the compression bulb. Connecting the vacuum system to the gauge, the weight is then raised filling the compression bulb with mercury, first trapping the gas contained within it and compressing in into the capillary tube. This effectively amplifies the system pressure. Knowledge of the bulb volume and capillary diameter allows a direct calibration.