A Galvanometer; but what was it for ?

 This instrument is a galvanometer, a meter used for balancing or testing an external electrical circuit. In the days before absolute measurements were reliable the method used was to connect a known fixed resistance, a battery, and a variable resistance across the circuit to be measured, in what was known as a "bridge" configuration. By altering the value of the variable resistance the resistance of the external circuit could be calculated. A galvanometer, which is a centre-zero meter, often a moving coil type, was connected so that positive and negative current could be balanced out. At the point where the meter read zero the variable resistance setting was read. Often this resistance was in the form of a box carrying plug-in shorting elements such that a very accurate value could be read by adding up the resistors not being shorted out.

 

 

 This meter is interesting in that the needle is not held in place by a hairspring but relies on reading centrally through gravity; that is when the case is resting in a vertical position. The top photo shows the meter lying on its back, hence the needle is askew.

The top is made from ebonite and is engraved with the words "INTy" and "QNTy". The "y" in both cases are superscripts. These abbreviations stand for "Intensity" and "Quantity", terms which were outmoded long before Victoria's reign was over. There is a small lever to the bottom right which has two positions, "1/5" and "F". Dial bezel, terminals and the carrying ring are all brass, the internal electrical fittings are copper and brass, and the case is a rough zinc casting.

The manufacturer is "WALTERS E.M.Co.LTD. LONDON"

Although knocked around a bit, the instrument appears to be in good order... but what was this model used for and when was it made?

I would hazard a guess that it was used to test detonator circuits, maybe in a coal mine?

Here's another Galvanometer

 An early example of a general purpose galvanometer. This particular type does not have a balanced needle and so must be operated in a vertical position. As meter design improved their pointers were balanced and the meter could be operated in any position. Compare the design of the pointer with the one above, which although not accurate in any position does at least have a symetrical pointer giving it better stability.

The case looks like mahogany and its construction is cheap.

The top terminals are brass and marked "Q", "I" and "IQ", which refer to Intensity (Voltage) and Quantity (Current). The scale is marked in degrees up to 90 to the left and to the right.

There's no maker's name anywhere on the instrument and I suspect it was manufactured before 1910 and not in the UK.

Can anyone identify it and for what it might have been used ?

Below is a similar example from Dave Brown in Christchurch NZ.

 Quote from Dave

"This one came from Telecom NZ-formerly NZPO- and I expect it had been used in that organisation waay back! Reason I say this is the terminals on the top have small round ivory labels inset in the box labelled INT and QTY- as any old PO engineer knows (guess where I used to work!) these stand for intensity and quantity-the old terms for voltage and current.
It has no back to the wooden box and the needle wont quite zero but its a fine example of the old I&Q meter that was the standard PO faultmans test meter in the early days. There were more modern metal cased versions made as well -not sure of the time frame for them but they did have range selection terminals rather than the single range for I and Q of these old ones."

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