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The Christian Philosopher; or, Science and Religion

Note VIII, p. 99.—Electro-Magnetic Machines

Note VIII, p. 99.—Electro-Magnetic Machines

The possibility of moving small pieces of mechanism by the action of the electro-magnetic power has been known for some time past, but it seems never to have been practically applied on a large scale until in 1837 it was adapted to the propulsion of a boat on the river Neva, by Professor Jacobi of Petersburg. On the 25th September, 1838, a galley, 28 feet in length and 7 1/4 in breadth, was provided with paddles similar to those of a steam vessel. The action was produced from 320 pair of plates, arranged along the sides of the galley, room being left for twelve persons. The vessel was made to proceed against the stream, and the speed attained in still water was three English miles per hour. The plan consisted in rapidly reversing the poles during the action—Since the above period a machine has been contrived by Mr. R. Davidson of Aberdeen, in which a reiterated series of attractions are employed to produce the effect. The following is a brief account of Mr. Davidson's experiments, abridgod from a letter of Professor Forbes of King's Col- page 153 lege, Aberdeen. Mr. R. Davidson has made an arrangement by which, with only two electromagnets, and less than one square foot of zinc surface (the negative metal being copper) a lathe is driven with such velocity, as to be capable of turning small articles. He has another arrangement by which, with the same small extent of galvanic power, a small carriage is driven, on which two persons are carried along a very coarse wooden floor of a room. He has likewise a third arrangement not yet completed, by which, from the imperfect experiments he has made, he expects to gain very considerably more force from the same extent of galvanic power than from either of the other two. The first two machines are exceedingly simple, without the least complexity, and therefore easily manageable, and not liable to derangement, and they take up very little room. As yet, the extent of power of which they are capable has not been at all ascertained, as the size of the battery employed is so trifling, and the magnets so few; but it seems probable that a very great power, in no degree inferior even to that of steam, but much more manageable, much less expensive, and occupying greatly less space—if the coals be taken into account—may be obtained. The Professor considers Mr. Davidson's inventions to be so interesting to railroad proprietors in particular, that it would be much for their interest to take up the subject and be at the expense of making the experiments necessary to bring this power into operation on a great scale.—The difference between Professor Jacobi's plan and Mr. Davidson's is this;—that Jacobi produces motion by changing the poles of the magnets, and Mr. Davidson, by cutting off the galvanic current at given points—the power of alternating as the rotation proceeds, from a neutralized magnet to a newly changed one. In both experiments it has been clearly demonstrated that the power of the magnet is increased, by increasing the diameter, and adding to the length of the helix. The power is also increased by increasing the size of the bars.