The medical and surgical uses of electricity, including the X-ray, Finsen light, vibratory therapeutics, and high-frequency currents / by A. D. Rockwell ... with two hundred and fifty-two illustrations.

Date:
1903
Catalogue details

Licence: In copyright

Credit: The medical and surgical uses of electricity, including the X-ray, Finsen light, vibratory therapeutics, and high-frequency currents / by A. D. Rockwell ... with two hundred and fifty-two illustrations. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    points to the north and the other to the south. If the magnet be disturbed in any way, and forced temporarily out of position, it at once and uni- formly returns. Polarity is a quality that belongs not only to magnetism, but also to other fonns of electricity, and to light and the other great forces. The poles of a magnet are always at its ends, for here the attractive power is greatest. This can be demonstrated by a very simple experi- ment. If a magnetic bar be rolled in a pile of iron filings, it will be found that these adhere to the bar most firmly and in the greatest quan- tity at or near its poles. The quantity that adheres is less as we approach the middle of the bar. Neutral Li?ie.—In long bars there is always a place at the middle, or near to it, where no filings are attracted. This space is variously termed the neutral or magnetic zone, or magnetic equator, or point of indiffer- ence. Another familiar experiment is to pass an iron ball, suspended by a string or thread, near to a magnet from end to end. It is observed that Fig. I. the ball is attracted very little, or not at all, in the middle, but that the attractive power is increased as we bring it toward either end. If any substance be placed between the ball and the magnet, the attraction is just as marked, unless the interposed substance itself contains iron. Nearly all substances that are not themselves magnetic are capable of transmit- ting the magnetic influence. Another feature of magnetic polarity is that like poles repel, and un- like poles attract, each other. If one magnetic bar be suspended freely in the air, and another be brought near to it, it will be found that the north pole of one is attracted by the south pole of the other, and vice versa—in short, that the like poles repel, while the unlike attract. Magnetism of Broketi Magnets.—If a bar that has been magnetized be broken in the middle, each half will have two poles and a neutral point in the centre. If one of these halves is broken in the middle, each half will be found to have two poles and a neutral line. If one of these parts in turn be broken, each half will again be found to be a complete magnet, with two poles and a neutral line, and so on as long as we can carry the division. Coulomb's Theory of Magnetism.—A theory of magnetism advanced by Coulomb is, that magnetic substances consist of particles, each one of