Phoning from a Trolley Car in 1896
Some interesting experiments have recently been tried by Mr. Kingsley l. Martin, assistant engineer on the New York and Brooklyn Bridge, in the line of establishing telephonic communication between moving trains and between trains and the train dispatcher's and bridge offices.
The necessity of some adequate method of train communication and signaling in cases of fog or some emergency has been felt, but there have been difficulties in the way of establishing telephonic communication with moving trains that have prevented it from being put into practice.
Mr. Martin has overcome these difficulties and has succeeded in communicating with moving trains with the same facility as between fixed points.
The bridge is provided with a trolley wire for electrically lighting the trains. This wire, which was used in the telephone experiment, was connected with the train dispatcher's office and with the bridge offices, and upon the cars were placed arms provided with compound brushes which touched the trolley wire.
The circuit was completed through the car truck and track rail, the connection between the circuit wires and truck being completed by a brush resting on one of the car wheels.
The compound brush consisted of a number of brushes of brush copper fastened together with intermediate pieces of soft rubber. The brushes being electrically connected with each other and with the telephone wire, arranged in this way, unbroken conversations could be carried on while the trains moved along.
The electrical contact of the compound brush with the trolley wire was so perfect that the sliding of the brush on the wire produced no noticeable effect.
It is proposed to permanently equip the cars with telephones and to provide a suitable electric conductor on the bridge in convenient position for contact with the brushes carried by the cars.
Scientific American article and engraving, April 4, 1896