SIR FRANCIS RONALDS has done well in republishing this ortion of his work, which was first printed in 1823. The hope which he expresses in the preface to this reprint that his name “may remain connected with an invention which has conferred incalculable benefits on mankind,” is quite justified by the experiments which he made and published many years before the final success of telegraphy. Sir Francis, before 1823, sent intelligible messages through more than eight miles of wire insulated and suspended in the air. His elementary signal was the divergence of the pith balls of a Canton's electrometer produced by the communication of a statical charge to the wire. He used synchronous rotation of lettered dials at each end of the line, and charged the wire at the sending-end whenever the letter to be indicated passed an opening provided in a cover; the electrometer at the far end then diverged, and thus informed the receiver of the message which letter was designated by the sender. The dials never stopped, and any slight want of synchronism was corrected by moving the cover. Hughes' printing instrument is the fully developed form of this rudimentary instrument. A gas pistol was used to draw attention, just as now a bell is rung. The primary idea of reverse currents is to be found where Sir Francis suggests that the wire when charged with positive electricity should discharge not to earth but into a battery negatively charged. Equally interesting is the discussion on what we now call lateral induction, then known as compensation. The author clearly saw that in the underground wires, which he suggests as substitutes for aerial lines, this induction would be or might be a cause of retardation. His own words must here be quoted:—“That objection which has seemed to most of those with whom I have conversed on the subject the least obvious, appears to me the most important, therefore I begin with it, viz., the probability that the electrical compensation, which would take place in a wire enclosed in glass tubes of many miles in length (the wire acting, as it were, like the interior coating of a battery) might amount to the retention of a charge, or, at least, might destroy the suddenness of a discharge, or, in other words, it might arrive at such a degree as to retain the charge with more or less force, even although the wire were brought into contact with the earth.” This passage, written in 1823, is very remarkable, and would alone entitle the author to be mentioned in any history of underground or submarine telegraphs. Testing-boxes were invented by Sir Francis, and a code is suggested by him. If these things had been mere suggestions they would have been remarkable, but accompanied by practical experiments proving that the scheme could be carried out, they ought to connect his name permanently with the history of the Electric Telegraph.
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