No.L-1788317 and L-128442
Cambridge Instruments pattern T meters Housed in polished wooden boxes. Moving coil instrument with additional scale and terminals for measuring alternating current in conjunction with a thermal junction. Scaled 0-150 millivolts at 500 ohms and 0-150 degrees [x 0.02] at 10 ohms. Note the Working. Cambridge Instrument Company Ltd, UK, date unknown.
This is one of many instruments collected by Jack Davidson C Eng FIEE which I have been given by Dr Graham Winbolt
Interior of the instrument
The meter is shunted by one resistor and wired in series with another to present 10 ohms to the terminals on the left, the right hand resistor is 490 ohms thus presenting 500 ohms to the millivolt terminals on the right. A typical Cambridge vacuojunction is pictured below [this one is open circuit and does not belong to this meter]