Elementary Lessons in Electricity & Magnetism

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Macmillan and Company, 1881 - Electricity - 446 pages
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Page 249 - I say, if these things are so, may not the knowledge of this power of points be of use to mankind, in preserving houses, churches, ships, &c. from the stroke of lightning, by directing us to fix on the highest parts of those edifices, upright rods of iron made sharp as a needle, and gilt to prevent rusting, and from the foot of those rods a wire down the outside of the building into the ground, or down round one of the shrouds of a ship...
Page 260 - The unit difference of magnetic potential exists between two points, when it requires the expenditure of one erg of work to bring a unit magnetic pole from one point to the other against the magnetic forces.
Page 249 - Would not these pointed rods probably draw the electrical fire silently out of a cloud before it came nigh enough to strike, and thereby secure us from that most sudden and terrible mischief?
Page 260 - ... currents in the neighbourhood, without the presence of a magnet. Since the peculiarity of the magnetic field consists in the presence of a certain force, we may numerically express the properties of the field by measuring the strength and direction of the force, or, as it may be worded, the intensity of the field and the direction of the lines of force.
Page 200 - The unit of surface is the square centimetre. Volume. — The unit of volume is the cubic centimetre. Velocity. — The unit of velocity is the velocity of a body which moves through unit distance in unit time, or one centimetre per second.
Page 201 - The unit of force is that force which, acting for one second on a mass of one gramme, gives to it a velocity of one centimetre per second.
Page 271 - ... unit difference of potential exists between two points when it requires the expenditure of one erg of work to bring a unit of -)- electricity from one point to the other against the electric force.
Page x - ... can neither create nor destroy electricity, though we may alter its distribution, may make more to appear at one place and less at another, may change it from the condition of rest to that of motion, or may cause it to spin round in whirlpools or vortices which themselves can attract or repel other vortices. According to this view all our electrical machines and batteries are merely instruments for altering the distribution of electricity by moving some of it from one place to another, or for...
Page 150 - Every portion of the circuit is acted upon by a force urging it in such a direction as to make it enclose within its embrace the greatest possible number of lines offeree.
Page 246 - Giving light ; color of the light ; crooked direction ; swift motion ; being conducted by metals ; noise in exploding ; conductivity in water and ice ; rending imperfect conductors; destroying animals; melting metals; firing inflammable substances ; sulphureous smell (ozone) ; and similarity of appearance between the brush discharge from the tips of masts and spars sometimes seen at sea, called St. Elmo's fire by the sailors, and the slow escape from points on an electrical machine or a leyden jar.

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