File:Practical electro-therapeutics and X-ray therapy - with chapters on phototherapy, X-ray in eye surgery, X-ray in dentistry, and medico-legal aspect of the X-ray (1912) (14757071165).jpg

Identifier: practicalelectro00mart (find matches)
Title: Practical electro-therapeutics and X-ray therapy : with chapters on phototherapy, X-ray in eye surgery, X-ray in dentistry, and medico-legal aspect of the X-ray
Year: 1912 (1910s)
Authors: Martin, James Madison, 1866-1947
Subjects: Electrotherapeutics X-rays Diagnosis, Radioscopic Eye Electric Stimulation Therapy X-Ray Therapy Ophthalmologic Surgical Procedures
Publisher: St. Louis : C.V. Mosby
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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ace of a permanent magnet, the smallcoil 1, or primary coil, is placed inside of coil a. The terminals ofcoil 1 are connected to the poles of the battery 2. So long as thecurrent remains unbroken or the coils remain stationary, no changeis noted in the galvanometer e. If, however, the battery currentis broken, the needle in the galvanometer will be deflected to one MAGNETISM AND ELECTROMAGNETISM 39 side, and when the battery circuit is closed the galvanometer needlewill be deflected to the other side. The distance that the galvanome-ter needle is deflected will depend upon the strength of the bat-tery current and the number of turns of wire on the two coils. Thechange in the direction of the needle at the breaking of the currentis caused by the change in the direction of the lines of force aroundthe conductors c and d. The electromagnetic influence of theprimary coil 1 on the secondary coil a is responsible for the currentdelivered to conductors o and d. This electromagnetic method of
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Fig. 11.—Starting an electric current with electro-magnetism. starting an electric current is the foundation principle of the far-adic coil as well as of all motors and dynamos. On account of the sudden magnetizing and demagnetizing prop-erty of soft iron, it is possible to construct a faradic coil in such amanner as to automatically change the magnetic field of the pri-mary coil by rapidly interrupting the battery current. Beforeproceeding farther, a thorough understanding should be had ofwhat has been said on the subject of magnetism and electromag-netism. The effect produced on the galvanometer by moving the per-manent magnet in and out of the coil, as illustrated in Fig. 10, hasbeen observed and a similar effect has been observed by making 40 PRACTICAL ELECTRO-THERAPEUTICS AND X-RAY THERAPY and breaking- the battery current in Fig. 11. In either ease a cur-rent is started in the secondary coil, but the method is too clumsyto be of any practical use. By making use of the rapid ma

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