It's a Weston D.C. Voltmeter, 125 Ohms per Volt:
I paid less than $5.00.
Sorry about the glare, had to use the flash.
The March '32 QST used as background is from my collection and features a nice one-tube Hartley oscillator-transmitter using a type '45 tube for the beginning ham. You thought low-power "QRP" operation was a new thing? Good old George Grammer tells us this transmitter "...will deliver 5 or 6 Watts to the antenna," right in the QRP range.