Collins Indicator

Here is another precision instrument in a beautiful wooden box, made by the Cambridge Scientific Instrument Company. The company was founded in the late 1870s by Robert Fulcher to service instruments for the Cambridge physiology department.

The device is a Collins Indicator, a pressure measuring instrument patented in England in 1922, designed to monitor and record the pressure changes inside an engine. From The Engine Indicator (John Walter); An indicator is a small, originally mechanically-operated instrument that gives an insight into the operation of a range of pressure-operated machines — steam engines, gas and oil engines, compressors, condensers, even guns — by comparing the rise and fall of pressure during the operating cycle. The use of an oscillating drum allows variations in pressure to be recorded on both the outward stroke and the return journey. Excepting some of the continuously-recording instruments and virtually all maximum pressure recorders, indicators usually give a trace in the form of a closed loop.

The description of this Collins device is on page 27 and 28 of the previous mentioned link.

The Canadian supplier is long gone...

Thanks, Glenn!