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) (14570432328).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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ION BETWEEN MAGNETS. All magnets possess one property in common—namely, that ofattraction and repulsion. Magnetism obeys the same laws thatgovern and control electricity—i. e., like poles repel and unlikepoles attract. An interesting experiment may be performed bymagnetizing two ordinary cambric needles and placing them ona smooth pane of glass. When placed with unlike poles together,they will hold each other, as it were, in a tight embrace, but whenthe poles are reversed they actually push each other apart. 34 PRACTICAL ELECTRO-THERAPEUTICS AND X-RAY THERAPY One piece of steel may be magnetized by a magnet no largerthan itself, both having the same magnetic strength. To do thisthe unmagnetized bar is stroked from center to end with one endof the magnet placed at right angles to the steel bar. Afterseveral strokes the bar is turned over and ends reversed, andwith the other end of the magnet the stroking is continued as be-fore. The steel bar will now be found to be magnetized, and
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Fig. 6.—Horseshoe magnet. N, north pole; S, south pole. will attract metallic objects the same as the magnet that magnet-ized it. To increase the influence of a bar magnet, it should bebent into the shape of a horseshoe, as shown in Fig. 6. In thehorseshoe magnet the distance between the poles is much shorterand the resistance offered by the air is not so great; therefore themagnetic field between the poles is much stronger. ELECTROMAGNETISM. While an electric current is going through a conductor, anotherinfluence is put in motion which passes in circles around the con-ductor and at right angles to it. This external force or manifesta-tion is called electromagnetism, and its strength depends upon thestrength of the current in the conductor. Fig. 7 illustrates thelines of magnetic force about a conductor. The presence of thisexternal force may be proven by placing a galvanometer eitherabove or below a wire carrying a current. The needle will be de-flected in proportion to the strengt

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