Electro-magnetism: History of Davenport's Invention of the Application of Electro-magnetism to Machinery... Also, Extracts from Other Public Journals...

Front Cover
G. & C. Carvill, 1837 - 94 pages

From inside the book

Common terms and phrases

Popular passages

Page 49 - Suppose that the two extremities of a cloud highly charged with electricity hang down towards the earth ; they will repel the electricity from the earth's surface, if it be of the same kind with their own, and will attract the other kind ; and, if a discharge should suddenly take place at one end of the cloud, the equilibrium will instantly be restored by a flash at that point of the earth which is under the other. Though...
Page 88 - Hence arises still further confirmation, if any were required, of the identity of common and voltaic electricity, and that the differences of intensity and quantity are quite sufficient to account for what were supposed to be their distinctive qualities.
Page 85 - ... to complete the circuit, these currents could not exist. Since the motion, not only of metals but even of fluids, when under the influence of powerful magnets, evolves electricity, it is probable that the gulf stream may exert a sensible influence upon the forms of the lines of magnetic variation, in consequence of electric currents moving across it, by the electro-magnetic induction of the earth.
Page 56 - There are places where the magnetic meridian coincides with the terrestrial meridian ; in these a magnetic needle freely suspended points to the true north; but if it be carried successively to different places on the earth's surface, its direction will deviate sometimes to the east and sometimes to the west of north. Lines drawn on the globe, through all the places where the needle points due north and south, are called lines of no variation, and they are extremely complicated.
Page 16 - But it is an important fact, discovered by experience, that the latter is soon impaired in its power by the influence of the revolving galvanic magnet, which is easily made to surpass it in energy, and thus, as it were, to overpower it. It is obvious, therefore, that the fixed magnet, as well as the revolving, ought to be magnetized by galvanism, and then there is every reason to believe that the relative equality of the two, and of course their relative energy, may be permanently supported, and...
Page 17 - The entire apparatus is therefore constructed of soft unmagnetic iron, which being properly wound with insulated copper wire, is magnetized in an instant, by the power of a very small battery. The machine is indeed the identical one used before, except that the exterior circle of permanent magnets is removed and in its place is arranged a circle of soft iron, divided into two portions to form the poles. These semicircles are made of hoop iron, one inch in width, and one eighth of an inch in thickness.
Page 80 - The electro-magnetic effect of the elective current induced in a conductor by a magnetic pole, in consequence of their relative motion, is such as tends continually to diminish that relative motion ; that is, to bring the moving bodies into a state of relative rest : so that, if the one be made to revolve by an extraneous force, the other will tend to revolve with it, in the same direction, and with the same velocity.
Page 48 - ... that they owe their existence, or at least their form, to that fluid. It is very probable that when two currents of dry air are moving different ways, the friction of the two surfaces may evolve electricity. Should these currents be of different temperatures, a portion of the...
Page 48 - When two clouds, charged with opposite kinds, approach -within a certain distance, the thickness of the coating of electricity increases on the two sides of the clouds that are nearest to one another ; and when the accumulation becomes so great as to overcome the coercive pressure of the atmosphere, a discharge takes place, which occasions a flash of lightning. The actual quantity of electricity in any...
Page 21 - Thomas Davenport. In the words of the patent, taken out, this invention " consists in applying magnetic and electro-magnetic power as a moving principle for machinery, in the manner described, or in any other substantially the same in principle.

Bibliographic information