Elements of Electricity, Magnetism, and Electro-magnetism: Embracing the Late Discoveries and Improvements, Digested Into the Form of a Treatise, Being the Second Part of a Course of Natural Philosophy, Compiled for the Use of the Students of the University at Cambridge, New England, Μέρος 2

Hilliard and Metcalf, 1826 - 395 σελίδες

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Σελίδα 87 - Normally the first production contract will have more changes than the second, the second more than the third, and so on.
Σελίδα 368 - ... of expense. The noise of the thunder generally occasions much alarm, although the danger is then passed ; it is over, indeed, on the appearance of the lightning, for any one struck by it neither sees the flash nor hears the report. The noise is never heard till after the flash, and its distance may be estimated at so many times 1136 feet as there are seconds between the appearance of the lightning and the sound of the thunder. Lightning often strikes solitary trees, because, rising to a great...
Σελίδα 366 - The general law or fact, in nature, so far as we can observe, is that all bodies attract each other in the direct ratio of their masses, and in the inverse ratio of the squares of the distances.
Σελίδα 370 - It is also advisable to have several paratonnerres round each magazine. If the magazine be in a tower, or other very lofty building, it may be sufficient to defend it by a double copper conductor, without any paratonnerre stem.
Σελίδα 368 - ... by it are frequently set on fire. No instance has yet occurred of an iron bar, of rather more than half an inch square, or of a cylinder of the same diameter, having been fused, or even heated red hot by lightning. A bar of this size would therefore be sufficient for a lightning-rod, but as its stem ought to rise from 15 to...
Σελίδα 369 - ... about 2^ inches square. • Iron being exposed to rust by the action of the air and moisture, the point of the stem is liable to become blunt; to prevent this, a portion is cut off from the upper end, about 20 inches in length, and replaced by a conical stem of brass or copper, gilt at its extremity^ or terminated by a small platina needle, two inches long.* The platina needle should be soldered with silver solder to the copper stem ; and to prevent its separating from it, which might sometimes...
Σελίδα 368 - When the lightning reaches the foot of the tree, it divides itself amongst the conductors that it finds near it, or strikes some in preference to others, according to circumstances, and sometimes it has been known to kill every animal that had sought shelter under the tree ; at others only a single one out of many has perished by the stroke. A...
Σελίδα 373 - These facts, together with ihe incapacity of the caloric fluid, extricated by the calorimotor, to permeate charcoal, next to metals the best electrical conductor, must sanction the position I assigned to it, as being in the opposite extreme from the columns of De Luc and Zamboni. For, as in these the phenomena are such as are characteristic of pure electricity, so in one very large galvanic pair, they almost exclusively demonstrate the agency of pure caloric.
Σελίδα 367 - This heat is sufficient to make a wire red-hot, or to fuse or disperse it, if sufficiently slender; but it scarcely raises the temperature of a bar of metal, on account of its large mass. It is by the heat of the electric current, as well as by that disengaged from the air, condensed by the passage of the lightning through it, when not conveyed by a good conductor, that buildings struck by it are frequently set on fire. No instance has yet occurred of an iron bar...

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