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THE 



POPULAR SCIENCE 



MONTHLY. 



JULY, 1903. 



HEETZIAN WAVE WIEELESS TELEGRAPHY. II. 



By Dr. J. A. FLEMING, F.R.S., 



PROFESSOR OF ELECTRICAL ENGINEERING, UNIVERSITY COLLEGE, LONDON. 



'\ XTE have next to consider the appliances for creating the neces- 

 ' » sary charging electromotive force, and for storing and releas- 

 ing this charge at pleasure, so as to generate the required electrical 

 oscillations in the aerial. 



It is essential that this generator should be able to create not only 

 large potential difference, but also a certain minimum electric current. 

 Accordingly, we - are limited at the present moment to one of two 

 appliances, viz., the induction coil or the alternating current trans- 

 former. 



It will not be necessary to enter into an explanation of the action of 

 the induction coil. The coil generally employed for wireless telegraphy 

 is technically known as a ten-inch coil, i. e., a coil which is capable of 

 giving a ten-inch spark between pointed conductors in air at ordinary 

 pressure. The construction of a large coil of this description is a matter 

 requiring great technical skill, and is not to be attempted without con- 

 siderable previous experience in the manufacture of smaller coils. The 

 secondary circuit of a ten-inch coil is formed of double silk-covered 

 copper wire, generally speaking the gauge called No. 36, or else Ko.. 

 34 S.W.G. is used, and a length of ten to seventeen miles of wire is 

 employed on the secondary circuit, according to the gauge of wire 

 selected. For the precautions necessary in constructing the secondary 

 coil, practical manuals must be consulted.* 



* Instruction for the manufacture of large induction coils may be obtained 

 from a ' Treatise on the Construction of Large Induction Coils,' by A. T. 

 Hare. (Methuen & Co., London.) 



VOL. LXTTT. — 13. 



