File:Practical radiography - a handbook for physicians, surgeons, and other users of X-rays (1901) (14571095959).jpg

Identifier: practicalradiogr00isen (find matches)
Title: Practical radiography : a handbook for physicians, surgeons, and other users of X-rays
Year: 1901 (1900s)
Authors: Isenthal, A. W Ward, H. Snowden (Henry Snowden), 1865-1911
Subjects: Radiography X-rays X-rays Radiography X-Rays
Publisher: London : Published for The Photogram, Ltd. by Dawbarn and Ward, Ltd.
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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any appreciabletime, and the induced secondary E.M.F. will therefore notbe lowered. We thus obtain in practice an alternatingcurrent of which the E.M.F. in one direction practicallyovershadows that in the other direction — that is, apulsating or uni-directional current such as we require forthe working of the ordinary Eontgen tubes. In order to ensure this suddenness of the break we mustendeavour to avoid or minimize the opening sparks whichtake place between the contact points of the interrupter ;this may be effected in various ways. Either the spark isblown away by means of an air-blast (mostly used inAmerica), or the energy represented by the spark isdeflected into a condenser, of large capacity (Fizeausmethod), the two coatings of which are connected to thetwo contact points of the interrupter. The spark energycharges the condenser, and the discharge of the lattertaking place previous to and during the closing of theprimary circuit, and being contrary in direction to the 2. >
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< Induction Coils and Interrupters 49 primary current, quickly destroys the core-magnetism, andstill further reduces the induced E.M.F. of the closingcurrent. One other point which must be attended to is thenecessity that the iron core quickly follows the magneticchanges to which the primary current subjects it.Practice has shown that only very soft iron can do this;besides, induction also takes place in the mass of the coreitself, resulting in the flow of Foucault and eddycurrents which would heat the core and thus wasteenergy. To overcome these currents, or rather to prevent themas far as possible, the iron core of an induction coil ortransformer is not made ,in one solid piece, but is sub-divided in a direction vertical to the flow of the eddy currents. With the foregoing theoretical considerations in mind,it will be easy to intelligently appreciate the constructivedetails of an induction coil, as described in the followingpages. (a) Induction Coils. Every induction coil is made

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