ID: 
788
Maker's Name: 
UNK
Where made: 
England
Dimensions: 
18 × 18 × 16 cm

This is a standard variable capacitor using interleaved metal plates, one set stators and one set rotors. Rotation of the shaft by the knob moves the stator plates in and out of the rotor plates. The capacitor scale is in the old units of Jars, varying from 0.05 to 0.95 jars. One Jar is about 200 picofarads.