The electric current : how produced and how used / by R. Mullineux Walmsley.

  • Walmsley, R. Mullineux (Robert Mullineux)
Date:
1894
Catalogue details

Licence: Public Domain Mark

Credit: The electric current : how produced and how used / by R. Mullineux Walmsley. Source: Wellcome Collection.

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    are at A, and the “ local ” switch-springs already referred to are at B, both within easy reach of the operator sitting in front of the table. At C are the switch-springs of all the subscribers on the exchange arranged in hundreds, in the manner partly shown in Fig. 321, so that any required spring can be quickly found. At D are the “ring-off” indicators —i.e. the indicators which show when the conversation is finished, and that the connections may be broken. The construction and mode of action of the “ indi- cators ” has still to be explained. Of these there are very numerous patterns, differing in minor, but sometimes im- portant, details. A very good one, known as the “ Danvers ” pattern, is shown in Fig. 326. A two-limb electro-magnet M, placed behind the indicator-board, has an armature A pivotted as shown, and with an extension passing through a slot in the framework. The front end of the lever is held depressed by a strong spring, which can be adjusted by the screw S, and which thus pulls the armature A off the magnet M when the current is not passing. At the end of this front arm is a catch, which usually engages with the top edge of and holds up the shutter P. But when A is