File:A manual of practical medical electricity - the Röntgen rays and Finsen light (1902) (14597030318).jpg

Identifier: manualofpractica00turn (find matches)
Title: A manual of practical medical electricity : the Röntgen rays and Finsen light
Year: 1902 (1900s)
Authors: Turner, Dawson
Subjects: X-Rays Electrophysiology Electrosurgery Electric Stimulation Therapy Electrotherapeutics X-rays Electrophysiology Electrosurgery
Publisher: New York : William Wood & Company
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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the two wattsout, even supposing that the machine is a perfect oneand that there is no loss. Now, the construction of themachine is such as to return us pur two watts in the formof volts rather than in that of amperes, say y^o ampere at200 volts. A transformer (p. 128) depends upon preciselythe same principles, but it acts the other way ; we put involts and get out amperes. We may apply the popularsaying about ordinary mechanical machines—that what isgained in power is lost in speed—by saying : What isgained in E. M. F. is lost in current-strength. In the Dubois-Reymond sledge-coil (Figs. 69 and 70)there is a stand, at one end of which is a strong upright,to which the primary coil is firmly attached, while thesecondary is arranged to slide in a groove along the stand,so that it can be made to approach, and if necessary com-pletely cover, the primary coil. A scale is attached tothe stand and a pointer to the secondary coil, so that the ii6 A Manual of Practical Medical Electricity
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Faradic Electricity 117 position in which the latter may be (the distance from theprimary coil) may be accurately noted. A bundle of soft iron wires covered with an insulatingvarnish, and enclosed in a light case, which is graduated,can be placed within or withdrawn to any required degree,according to the graduations, from the primary coil. Thisforms an electro-magnet, which is more rapidly magnetiz-able and demagnetizable than a solid one would be,because the induction currents, which would be set incirculation in a solid rod, are partly eliminated. The primary coil is wound with a few turns of thickwire to diminish resistance and self-induction. The secondary coil is wound with very many turns of

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