Tall's Distance Indicator
Tall's Distance Indicator was an electrical shipboard transmitter/receiver pair created by Mr. Tall, electrician in Vernon c. 1885, which could convey distances from 300 to 3700 yards. Such equipment would eventually be termed Range Transmitters and Receivers.
Design and Evaluation
Tall's transmitter had a handle at the base which could only be turned clockwise and rotated a contact wheel within the device with as many indentations as there were numbers on the face. In this instance, the number was 35 (300 to 3700 yards, in 100 yard increments, inclusive of both figures). The remote receiver had a bell which would ring continuously when new ranges were sent – a key on the side of the receiver could be depressed to break the bell's circuit and acknowledge receipt of the information, this action also causing an indication on a galvanometer atop the transmitter.
Battery cells were required at both the transmitter and receiver. The transmitter had what was apparently an on/off switch mounted on its right side. Four conductors were required between the transmitter and receiver.
By 1886, Tall's devices were being evaluated alongside several competitors, such as a Mr. Gisborne's and Lieutenant Lloyd's. Though the trials were still underway, Mr. Tall's devices were deemed "ingenious".
- Annual Report of the Torpedo School, 1885. Plate 29.
- Annual Report of the Torpedo School, 1885. p. 75.
- Annual Report of the Torpedo School, 1885. pp. xxv, 75.
- Annual Report of the Torpedo School, 1886. p. xiv.
- H.M.S. Vernon. Annual Report of the Torpedo School, 1885. Copy 21 at The National Archives. ADM 189/5.