1851 Great Exhibition: Official Catalogue: Class X.: William Alexander
426. ALEXANDER, WILLIAM, F.R.S.E., 52 West Register Street, Edinburgh — Inventor.
Model of an electro-magnetic telegraph, worked by means of voltaic currents through metallic conductors, deflecting magnetic needles, and thus unveiling the letters of the alphabet in the order required for any communication. The model was exhibited at the meeting of the Royal Scottish Society of Arts, on 15th November, 1837, after previous experiments throughout the year, to test the practicability and efficiency of the plan, made through a metallic circuit of four miles in the chemistry class-room of the University of Edinburgh. It is believed by the inventor to be the first definite plan for an electromagnetic telegraph ever shown in operation before the public or a scientific society. In 1837, the applicability of electro-magnetism to telegraphic purposes was matter of doubt and uncertainty, and the object of the inventor was to solve the problem by apparatus of the most simple construction, and which might lead to future improvements. The perfection to which electric telegraphs have since arrived, their superiority over all other methods for conveying intelligence between distant places, and their inconceivable importance and utility, are now well known and established, and are justly considered one of the wonders of the age. The following cut represents this early telegraph.
A is a voltaic battery; B, a trough filled with mercury; C, a wire connecting the zinc plate in the battery with the trough of mercury; D, the return wire connected with the copper plate of the battery; E, a key to be pressed down by the finger of the operator, like the key of a pianoforte; F, is a pendant wire which dips into the mercury when the key is depressed, and completes the circuit formed by the wires C and D, extending from one terminus of the telegraph to the other.
G is the distant dial upon which the whole letters of the alphabet and stops are marked. These are not seen
when the magnetic needles—poised horizontally in free space behind the dial—are in their natural position of North and South, with screens or veils marked V, attached to each of their North poles, and concealing the letters, but when the circuit is completed by the depression of the key E, the corresponding magnetic needle is deflected to the West, and exposes, as at K, the letter previously concealed. Thirty copper wires and a return wire extend from the keys to the magnetic needles.
A metallic rod may be advantageously substituted for the trough of mercury below the keys.
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