and detecting criminals had been signally demonstrated, and it was soon
adopted on a more extensive scale.

In 1845 Wheatstone introduced two improved forms of the apparatus,
namely, the 'single' and the 'double' needle instruments, in which the
signals were made by the successive deflections of the needles. Of
these, the single-needle instrument, requiring only one wire, is still
in use.

In 1841 a difference arose between Cooke and Wheatstone as to the share
of each in the honour of inventing the telegraph. The question was
submitted to the arbitration of the famous engineer, Marc Isambard
Brunel, on behalf of Cooke, and Professor Daniell, of King's College,
the inventor of the Daniell battery, on the part of Wheatstone. They
awarded to Cooke the credit of having introduced the telegraph as a
useful undertaking which promised to be of national importance, and to
Wheatstone that of having by his researches prepared the public to
receive it. They concluded with the words: 'It is to the united
labours of two gentlemen so well qualified for mutual assistance that
we must attribute the rapid progress which this important invention has
made during five years since they have been associated.' The decision,
however vague, pronounces the needle telegraph a joint production. If
it was mainly invented by Wheatstone, it was chiefly introduced by
Cooke. Their respective shares in the undertaking might be compared to
that of an author and his publisher, but for the fact that Cooke himself
had a share in the actual work of invention.

In 1840 Wheatstone had patented an alphabetical telegraph, or,
'Wheatstone A B C instrument,' which moved with a step-by-step motion,
and showed the letters of the message upon a dial. The same principle