'
The 'fresh systems' referred to was his 'mechanical' telegraph,
consisting of two letter dials, working synchronously, and on which
particular letters of the message were indicated by means of an electro-
magnet and detent. Before the end of March he invented the clock-work
alarm, in which an electro-magnet attracted an armature of soft iron,
and thus withdrew a detent, allowing the works to strike the alarm.
This idea was suggested to him on March 17, 1836, while reading Mrs.
Mary Somerville's 'Connexion of the Physical Sciences,' in travelling
from Heidelberg to Frankfort.
Cooke arrived in London on April 22, and wrote a pamphlet setting forth
his plans for the establishment of an electric telegraph; but it was
never published. According to his own account he also gave considerable
attention to the escapement principle, or step by step movement,
afterwards perfected by Wheatstone. While busy in preparing his
apparatus for exhibition, part of which was made by a clock-maker in
Clerkenwell, he consulted Faraday about the construction of electro-
magnets, The philosopher saw his apparatus and expressed his opinion
that the 'principle was perfectly correct,' and that the 'instrument
appears perfectly adapted to its intended uses.
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