Prototype Cox selenium-cell magnifier equipment, made by Kenwrick Cecil Cox, 1912-1920. Comprises: selenium cells nos. 4 and 5 (in wooden boxes); two experimental selenium cells (one in wooden box, one in cardboard box); two galvanometers (in one box); spare galvanometer coil and mirror, extra suspension spring (in cardboard box inside galvanometer box); seven grid slides, seventeen wire-wound resistors; four lenses.
This magnifier was invented by Kenwrick Cecil Cox, a British engineer who worked in a cable station in the Pacific ocean, on the Pacific Telegraph Cable. The purpose of the magnifier was to cut out the expensive and arduous task of re-sending messages that passed through the cable station on their way to other destinations. This was required because the signals lost clarity over distances of hundreds of miles, meaning that the only way for the messages to reach their destination was for operators to resend the messages manually when they passed from one length of cable to another. The magnifier boosted the signal strength and clarity. The regenerated signal was then suitable for perforating a new tape, or could be transmitted directly. These components are parts of the development prototypes made by Cox, largely in his spare time while working at various cable stations. The production version was in widespread use for over a decade.