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The induction coil has always been a popular piece of apparatus with amateurs and students interested in electrical science, so numerous and so fascinating are the experiments which can be performed with its aid. Its practical importance has, moreover, been considerably enhanced in re cent years by its application to such useful pur poses as X-ray work, wireless telegraphy, and the ignition of the charge in internal combustion engines, such as the petrol motors now so exten sively used for cycles and automobiles. In the following pages we have adhered to the lines usually adopted in this series of handbooks, and have commenced by giving sufficient theoretical information to enable the reader to understand the various principles involved in the design and construction of satisfactory apparatus. This is followed by descriptions of the methods of build ing coils for various purposes, and in a later chapter tables of dimensions are given which will enable the reader to construct a coil of any size, within limits, to suit his own Special requirements, if.
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