File:A manual of practical medical electricity - the Röntgen rays and Finsen light (1902) (14596995079).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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^ Amperesrule : Suppose yourself to be swimming with the current withyour face to the needle, then the north-seeking pole of theneedle will be deflected towards your left hand. In dealing with the comparatively large current pro-duced by one Leclanche cell on short circuit (some 300m.a.), the deviations of the needle can be easily seen ; butwhen we come to currents only y^o or -^\ as strong, as ingalvanization, the deflections would be so slight as to bealmost valueless, and some means of increasing them mustbe adopted if our instrument is to be of use to us. In galvanometers for medical practice, this is usuallydone by increasing the number of times the current hasto pass along the needle by coiling the insulated wirewhich carries it round the needle. Here the effect will benearly equal to the effect produced by one coil multiplied 6
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Measurement of Current-Strength 83 by the number of coils—nearly, because the position ofeach subsequent coil with reference to the needle cannotbe in so advantageous a position as the first turn, and,moreover, the needle is not equally deflected by each equaladdition of current-strength, because its poles, in beingdeflected, pass further and further from the influence ofthe coils. Tangent and sine galvanometers are instruments so con-structed that the tangent of the angle of deflection in theone case, and the sine of the angle through which the coilhas to be turned in the other case, are proportional to thestrength of the current. In galvanometers for physiological purposes, a means ofrendering the instrument even more sensitive must beemployed, and since the position which the needle takesup in the ordinary galvanometer is the resultant of twoforces—viz., the strength of the current, and the earthsmagnetic force—the greatest deviation is to be obtainedwhen the former is as str

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