File:A manual of practical medical electricity - the Röntgen rays and Finsen light (1902) (14597032148).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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much increases the total efficiency. Themodern dynamo is constructed upon the same principle,an electro-magnet being substituted for the permanentmagnet, and the coil of both magnet and armature putinto connection. The advantage the small magneto-electric machines haveover the ordinary battery or coil is that they are alwaysready, rarely get out of order, are very portable, andrequire no attention ; they are therefore useful in emer-gencies. Further, the current they yield is less painful Faradic Electricity 121 and stimulating than that from an induction coil. Theiradvantages are more than counter-balanced by the labourof turning them, and the difhculty of maintaining any-thing like a uniform strength of current. Mons. dArsonvals modification of the ordinary mag-neto-electric machine permits of an alternating currentwith sinusoidal variations. In the ordinary machine thevariations of the current are not uniform ; a glance at thediagrams (Fig. 73) taken from Mons. dArsonvals tracings
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Fig. 72)- — Curves to Represent the Currents of Magneto-Electric Machines. will exhibit this. The first tracing demonstrates thecurves of the alternating electrical waves yielded by a goodordinary magneto-electrical maehine, the second those ofa similar machine provided with a commutator to turn allthe currents into the same direction. This object hasevidently not been fully attained. The third representsthe sinusoidal variations of Mons. dArsonvals machine.The coils in this machine are fixed, and a circular steelmagnet is revolved by cogwheels before them. The 122 A Manual of Practical Medical Electricity current is taken from the two extremities of the coils, andall collectors and commutators are dispensed with. Thecurrent so obtained is extraordinarily smooth ; there areno breaks in it, and the alternating waves are perfectlyuniform. These properties render it valuable in thera-peutics. Dynamo Currents. The dvnamo is merely an improved magneto-electricmachine. In the current from

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