[8] 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.) Also see Vol. II. of "The Alternate-Current Transformer," by J. A. Fleming, chap. I. ("The Electrician" Printing and Publishing Co., 1, 2 and 3, Salisbury-court, Fleet-street, London, E.C.) [9] See "The Alternate-Current Transformer," by J. A. Fleming. Vol. I., p. 184. [10] Du Moncel states that MacGauley of Dublin independently invented the form of hammer break as now used. See "The Alternate-Current Transformer," Vol. II. chap. I. J. A. Fleming. [11] See Professor J. Trowbridge, "On the Induction Coil" _Phil. Mag._, April, 1902 Vol. III., Series 6, p. 393. [12] See Dr. Wehnelt's article in the _Elektrotechnische Zeitschrift_, January, 1899. [13] See _The Electrician_, Vol. XLII., 1899, pp. 721, 728, 731, 732 and 841; communications from Mr. Campbell Swinton, Professor S. P. Thompson, Dr. Marchant, the author and others; also p. 864, same volume, for a leader on the subject; also p. 870, letters by M. Blondel and Professor E. Thomson. See also _The Electrician_, Vol. XLIII., p. 5, 1899, extracts from a Paper by P. Barry; _Comptes Rendus_, April, 1899. See also the _Electrical Review_, Vol. XLIV., p. 235, 1899, February 17. [14] See _The Electrician_, Vol. XLII., 1899. [15] For a discussion of the function of the condenser in an ordinary induction coil, see "The Alternate-Current Transformer," by J. A. Fleming. Vol. II., p. 51. [16] See Lord Rayleigh, _Phil. Mag._, December, 1901. [17] It has sometimes been stated that the spark balls must be _solid_ metal and no hollow, but this is a fallacy, and has been disproved by Mr. C. A. Chant. See "An Experimental Investigation into the Skin Effect in Electrical Oscillators," _Phil. Mag._, Vol. III., Sec. 6, p. 425, 1902. [18] See _Proc._ Roy. Soc., London, February 23 and April 12, 1860; or reprint of Papers on electrostatics and magnetism, p. 247. [19] See _Phil. Mag._, August, 1902, Vol. IV., p. 224, 6th Series. Mr. Jervis-Smith has also described an experiment to show how much the use of compressed air round a spark gap is of advantage in working an ordinary Tesla coil. In his British specification, No. 12,039 of 1896, Mr. Marconi had long previously mentioned the use of compressed air round the spark gap. [20] This energy storage is at the rate of 44 foot-pounds per cubic foot of glass. This figure shows what a relatively small amount of energy is capable of being stored up in the form of electric strain in glass. In the case of an air condenser, it is only stored at the rate of 1 foot-pound per cubic foot. [21] See British specification No. 7,777 of 1900.--G. Marconi. "Improvements in Apparatus for Wireless Telegraphy."