This key, a Swiss PTT design, was made by Gustav Hasler of Bern, Switzerland.
Hasler was started by Dr. Gustav A. Hasler (1850 - 1900) and Heinrich Albert Escher and traces its origin to 1865
from the Eidgenössischen Telegraph works.
Although a Swiss PTT standard and manufactured for at least fifty years, this particular key dates approximately 1920.
The design was used not only by the Swiss Post Office, but also by the Swiss Army and Swiss railroads.
Notice the lower contacts.
They rest of a leaf spring made of steel. This contact design appears on other keys manufactured in Europe, including keys from Germany, and Denmark.
The leaf spring contacts are explained in "Un Siecle De Telecommunications En Suisse 1852-1952 Volume 1, Telegraphy," published by the Swiss PTT.
When and where silent contacts were first used is not known. However we do know that the design was used by Siemens and Halske of Germany
for their keys starting in 1871.
In Faszination Morsetasten: German telegraph keys Collector's guide, the keys are referred to as "geräuschlose" or "lautlose" keys, meaning "noiseless or "quite" keys. There are many World War Two era German military keys employing the leaf spring design.The leaf spring contact design was used through the 1950s and
beyond in several countries including East and West German, Switzerland and China.
Why were silent contacts needed?
Since these keys are quite large, made in large numbers and used by the Swiss PTT, we can assume that they were not made for clandestine or secret operations.
The German Telegraph Administration use the "lautlose" keys in larger offices. It is then probable this design was favored where there were many operators in a room.
The silent contacts would reduce the noise in a telegraph office and hence enable an operator to better copy his own sending. In most European landline circuits,
the sounder, if present, was in the circuit only on receive; on transmit, the operator listened to the clicking of his own key and / or watched the galvanometer swing
in order to monitor his own sending.
(Many European landline circuits did not use telegraph sounders; they used Morse register to record the incoming signals with ink on paper tape,
later to be transcribed by an operator.)
A Hasler catalog dated 1898 shows a line drawing of the silent key's brother. Also shown in the catalog are galvanometers and Morse registers,
both essential for a telegrapher's operating position in Europe at the turn of the century.
