“The deviation of the needle is the same, whether the uniting wire, instead of being immediately above the needle, be placed somewhat to the east or west of it, provided it continue parallel to and also above it. This shows that the effect is not the result of a simple attractive or repulsive influence, for the same pole of the magnetic needle which approaches the uniting wire, when placed on its east side, recedes from it when placed on its west side.”
[20] “Soon after this important discovery of Oersted’s was made, M. Ampère established the second fundamental law of electro magnetism, that the two conducting wires from the poles of the battery, when conveniently suspended, attracts each other when they transmit electrical currents moving in the same direction, and repel each other when the currents which they transmit have opposite directions.
“On the 25th Sept. 1820, M. Arago communicated to the French Institute the important discovery that the electrical current possesses, in a very high degree the power of developing magnetism in iron or steel. Sir H. Davy communicated a similar fact to Dr. Wollaston on the 12th of November, 1820, and Dr. Seebeck laid before the Royal Academy of Berlin a series of experiments on the same subject.
“M. Arago found that the uniting wires of a powerful Voltaic battery attracts iron filings often with such force as to form a coating around the wire ten or twelve times thicker than itself. This attraction, as he found, did not originate in any magnetism previously possessed by the iron filing, which he ascertained would not adhere to iron, and that it was not a case of common electrical attraction, was evident from the fact that copper and brass filings were not attracted by the uniting wire. M. Arago likewise found, that the iron filings began to rise before they came in contact with the uniting wire; and hence he drew the conclusion, that the electric currents converted each small piece of iron into a temporary magnet. In following out this view, the French philosopher converted large pieces of iron into temporary magnets and also small steel needles into permanent ones, (by employing the helix.) Sir H. Davy and Dr. Seebeck obtained analogous results without knowing what had been previously done in France.
“A galvanometer was first constructed by Professor Schweigger, of Halle, very soon after the first discovery of electro magnetism, and by him called an electro magnetic multiplier.”
In the year 1820, Ampère predicted the possibility of making the deflection of the magnetic needle, by the agency of the galvanic fluid, serve the purposes of transmitting intelligence. In page 19 of his memoir, he thus resolves the problem:
“As many magnetic needles as there are letters of the alphabet,” he says, “which may be put in action by conductors; which may be made to communicate successively with the battery by means of keys; which may be pressed down at pleasure, might give place to a telegraphic correspondence which would surmount all distance and would be as prompt as writing speech to transmit thought.”
“The next step in the progress of discovery, was that of making magnets of extraordinary power by means of a galvanic battery. This seems to have been first accomplished by Prof. Moll, of Utrecht, and Professor Henry, of Princeton, who was able to lift thousands of pounds weight by his apparatus.”
The following Extract is taken from a Work on Electro Magnetism
published by Jacob Green, M. D. Professor of Chemistry in
Jefferson Medical College, 1827.
“In the very early stage of electro magnetic experiments, it had been suggested, that an instantaneous telegraph might be constructed by means of conjunctive wires, and magnetic needles. The details of this contrivance are so obvious, and the principles on which it is founded so well understood, that there was only one question which could render the result doubtful. This was, whether by lengthening the conjunctive wires, there would be any diminution in the electrical effect upon the needle. It is the general opinion, that the electrical fluid, from a common electrical battery, may be transmitted, without any sensible diminution, instantaneously, through a wire three or four miles in length. At the philosophical dinner, as it has been called, got up a number of years ago by some gentlemen of Philadelphia, on the banks of the Schuylkill, it may be recollected that Dr. Franklin killed a turkey with the electric shock, transmitted across the river, a distance of more than half a mile; and Dr. Watson, who was also at the pains of making some experiments of this kind, asserts that the electric shock was transmitted, instantaneously, through the length of 12,276 feet. Had it been found true that the galvanic fluid could be transmitted in a moment through a great extent of conducting wire, without diminishing its magnetic effect then no question could have been entertained as to the practicability and importance of the suggestion adverted to above, with regard to the telegraph. Mr. Barlow, of the Royal Military Academy, who has made a number of successful experiments and investigations in electro magnetism, fully ascertained that there was so sensible a diminution with only 200 feet of wire, as to convince him at once of the impracticability of the scheme.