ELECTRO-MAGNETISM. (MOTIVE POWER oF.) Numerous attempts have been made to apply electromagnetism as a power for moving machines, and parti cularly by the apparatus employed by Jacobi, Dal Negro, M'Gauley, Wheat stone, and the machines recently con structed by Mr. Itiorth. However, not withstanding the talent which has been devoted to this interesting subject, and the large amount of money which has been spent in the construction of ma chines, the public are not yet in posses sion of any electro-magnetic machine which is capable of exerting power eco nomically.
The most remarkable experiments are those of Professor Jacobi, who, in 1838 and '39, succeeded in propelling a boat upon the Neva at the rate of four miles an hour.
Mr. Hiorth's engine embraces many new features that promise to render the power more effective than hitherto. One of the electromagnets made for the large engine, in a recenl trial, supported near ly 5000 lbs., and its attractive force at 1. of an inch was equal to nearly 1500 lbs. As this force can be multiplied without limits, it is reduced to a question of econ omy and convenience.
The power of electromagnets can be increased without limitation. A voltaic currentproduced by the chemical distur bance of the elements of any battery no matter what its form may be, is capable of producing by induction a magnetic force, this magnetic force being always in an exact ratio to the amount of matter (zinc, iron, or otherwise) consumed in. the battery.
The greatest amount of magnetic force is produced when the chemical action is most rapid.
Hence, in all machines, it is morn economical to employ a battery of intense action, than one in which the chemical action is slow. It has been proved by Mr. Joule, and most satisfactorily con firmed by Mr. R. Hunt, that one-horse power is obtainable in an electro-magnetic engine, the most favorably constructed to prevent loss of power, at the cost of 45 lbs. of zinc, in a Grove's battery, in 24 hours, while 15 lbs. are consumed in the same time to produce the same power in a battery of Daniell's construction. The intensity of Daniell's battery being f that of Grove's. The cause of this was referred to the necessity of producing a high degree of excitement, to overcome the resistance which the molecular forces offer to the electrical perturbations, on which the magnetic force depends.
What amount of magnetic power can• be obtained from an equivalent of any material consumed ? The following, re garded as the most satisfactory results yet obtained :-1. The force of voltaic current being equal to 673, the number of grains of zinc destroyed per hour was 151, which raised 9000 lbs. one foot high in that time. 2. The force of current being, relatively, 1300, the zinc destroyed in an hour was 291 grains, which raised 10,030 lbs. through the space of one foot.
3. The force being 1000, the zinc con sumed was 223 grains ; the weightlifting' one foot 12,672 lbs. The estimations made by :Messrs. Scoresby and Joule, and the results obtained by Oersted, and more recently by Mr. Hunt, very nearly' agree • and it was stated that one grain of coal consumed in the furnace of a Cor nish engine lifted 143 lbs. one foot high, whereas one grain of zinc consumed in the battery lifted only 80 lbs. The cost of 1 cwt. of coal is under 9d. ; the cost of 1 cwt. of zinc is above 216d. There fore, under the most perfect conditions, magnetic power must be nearly 25 times more expensive than steam power. But the author proceeded to show that it was almost proved to be an impossibility ever to reach this, owing, in the first place, to the rate with which the force diminishes through space. As the mean of a great many experiments on a largo variety of magnets, of different forms and modes of construction, the following result was given : Magnet and armature in contact, lbs.
lifting force - - - - 220 distant 1-250 of an inch 90 6 tt " 1-125 " 50 7 " 1-63 " 501 44 " 1-50 " 40 5 Thus at one-fiftieth of an inch distance four-fifths of the power is lost. This great reduction of power takes place when the magnets are stationary. Mr. R. Hunt has also shown that the moment they were set in motion a great reduction of the original power immediately took place ,• that, indeed, any disturbance pro duced near the poles of a magnet dimin ished, during the continuance of the mo tion, its attractive force. The attractive force of a magnet being 150 lbs. when free of disturbance, fell to one-half, by occasioning an armature to revolve near its poles.- Therefore, when a system of magnets which had been constructed to produce a given power is set in revolu tion, every magnet at once suffers an im mense loss ofpower, and consequently their combined action falls in practice very far short of their estimated power. This fact has not been before distinctly stated, although it is well known that Jacobi observed it. And not merely does each magnet thus sustain an actual loss of power, but the power tkus lost is converted into a new form of force, or or rather becomes a current of electri city, acting in opposition to the primary current by which the magnetism is in duced. prom an examination of all these results, Mr. Hunt is disposed to regard electromagnetic power as impracticable, on account of its cost, which must neces sarily be, he conceives, under the best conditions, fifty times more expensive than steam power, and is at present at least 150 times as expensive.