. Radiography and radio-therapeutics . f efficiency from the induc-tion coil the aim is to magnetise the core slowly (at make), and demagnetiseit rapidly (at break), the spark length depending ui)on the rapidity withwhich the core can be magnetised, the output of the coil upon the degreeof magnetisation. The size of the core depends upon the size of the primary and the THE INDUCTION COIL 17 current passing through it, and on the frequency and character of thebreak and the output arranged for. The modern heavy discharge coil has a very large and stout iron core,generally made up of sheets of me
. Radiography and radio-therapeutics . f efficiency from the induc-tion coil the aim is to magnetise the core slowly (at make), and demagnetiseit rapidly (at break), the spark length depending ui)on the rapidity withwhich the core can be magnetised, the output of the coil upon the degreeof magnetisation. The size of the core depends upon the size of the primary and the THE INDUCTION COIL 17 current passing through it, and on the frequency and character of thebreak and the output arranged for. The modern heavy discharge coil has a very large and stout iron core,generally made up of sheets of metal, whose length is five or six times itsdiameter or even more. The chief objects in core design are, (a) to diminish the inverse current,and (6) to reduce the losses due to eddy currents. The inverse currentis lessened by packing as much iron as possible into the space allowed forthe core. Eddy currents are reduced by using, instead of a solid ironcore, packed wires or plates varnished to diminish the electrical contactbetween Fig. 6.—Plau of winding of coil (primarj-, secondary), and connectionto condenser and break. (Newton & Wright.) The Primapy.—The primary consists of a number of turns of a thickcopper wire wound roimd the core. The primary coil is usually wound inthree layers, either as a simple winding, or, as is more common, as an adjust-able winding to allow of adaptability to meet prevailing conditions. Three methods of winding the primary are employed : (1) The connections are so arranged that each of the three layers canbe put in series or parallel with the others. These are connected up toterminals at one end of the coil and serve to vary the quantity of currentin the primary. They may be wired up to a switch-table and controlledfrom there, so that the operator may select the winding most suitable forthe work required. (2) The winding is arranged so that the coils can be tapped to permitconnection with different parts of the primary circuit. (3) The pr
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