[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 b.a.l.l.s 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 gla.s.s. This figure shows what a relatively small amount of energy is capable of being stored up in the form of electric strain in gla.s.s. 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."

[22] That this number really does represent the order of this oscillation frequency in an aerial has been shown by C. Tissot, _Comptes Rendus_, 132, p. 763, March 25, 1901, by photographs taken of the oscillatory spark of a Hertzian wave telegraphic transmitter. (See _Science Abstracts_, Vol. IV., Abs. 1,518.) He found frequencies from 05 million to 16 million.

[23] The term "jigger" is one of those slang terms which contrive to effect a permanent attachment to various arts and crafts. Similarly, the word "booster" is now used for a step-up or voltage-raising transformer or dynamo, inserted in series with an electric supply main. The word "boost" is a slang term signifying to raise or lift up. "To give a real good boost" is an expression for lending a helping hand. The term "jigger," in the same manner, is an adaptation of a seaman's term for hoisting tackle or lift.

[24] The "earth" itself probably only conducts electrolytically. All such materials as sand, clay, chalk, etc., and most surface soils are fairly good insulators when very dry, but conduct in virtue of moisture present in them.

[25] _The Electrician_, Vol. XL., p. 86 (leader).

[26] British Patent Specification, C. and S. A. Varley, No. 165, 1866.

[27] See also _Journal de Physique_, Vol. V., p. 573, 1886.

[28] See _Comptes Rendus_, Vol. CXI., p. 785; Vol. CXII., p. 112, 1891; or _La Lumiere Electrique_, Vol. XL., pp. 301, 506, 1891; or _The Electrician_, Vol. XXVII., 1891, pp. 221, 448.

[29] See _The Electrician_, Vol. XXIX., 1892, pp. 397 and 432.

[30] Mr. W. B. Croft, _Proc._ Phys. Soc., Vol. XII., p. 421. Report of meeting on October 27, 1893.

[31] See Professor Minchin, _Proc._ Phys. Soc., November 24, 1893; or _The Electrician_, Vol. x.x.xII., 1893, p. 123. See also Professor Minchin, _Phil Mag._, January, 1894, Vol. x.x.xVII., p. 90, "On the Action of Electromagnetic Radiation on Films containing Metallic Powders."

[32] This lecture was afterwards published as a book, the first edition bearing the same t.i.tle as the lecture--viz., "The Work of Hertz and Some of His Successors." In the second edition, published in 1898, an appendix was added (p. 59) containing "The History of the Coherer Principle," and the original t.i.tle of the work had prefixed to it "Signalling Without Wires."

[33] See _The Electrician_, Vol. XXVII., p. 222, 1891. E. Branly, "Variations of Conductivity under Electrical Influence."

[34] See _The Electrician_, Vol. XL., p. 90. Sir Oliver Lodge, "The History of the Coherer Principle."

[35] See Professor E. Branly, "A Sensitive Coherer," _Comptes Rendus_, Vol. Cx.x.xIV., p. 1,187, 1902; or _Science Abstracts_, Vol. V., p. 852, 1902.

[36] This device of making the inter-electrode gap in a tubular filings coherer wedge-shaped has been patented again and again by various inventors. See German patent No. 116,113, Cla.s.s 21a, 1900. It has also been claimed by M. Tissot.

[37] See _The Electrician_, Vol. XXVII., 1891, p. 448.

[38] _Journal_ of the Russian Physical and Chemical Society, Vol.

XXVIII., Division of Physics, Part I., January, 1896.

[39] See British Patent Specification No. 12,039, June 2, 1896.

[40] British Patent Specification No. 19,710 of 1899.

[41] _Comptes Rendus._, Vol. CXXVIII., p. 1,225, 1889; _Science Abstracts_, Vol. II., p. 521.

[42] _Il Nuovo Cimento_, Vol. X., p. 279, 1899.

[43] _Wied Ann._, Vol. LXVIII., p. 594, 1899; _Science Abstracts_, Vol.

II., p. 757.

[44] _Comptes Rendus_, Vol. Cx.x.x., p. 902, 1900; _Science Abstracts_, Vol. III., p. 615.

[45] See _Proc._ Roy. Soc., London, Vol. LXXI., p. 402.

[46] See Report by Capt. Quintino Bonomo, "Telegrafia Senza Fili," Rome, 1902; _L'Elettricista_, Ser. II., Vol. I., pp. 118, 173.

[47] See Royal Inst.i.tution, Friday evening discourse, by Mr. Marconi, June 13, 1902; also _The Electrician_, Vol. XLIX., p. 490; also a letter to _The Times_ of July 3, 1902, by the Marchese Luigi Solari.

[48] See U.S.A. Patent Specification No. 700,161, May 24, 1900.

[49] See E. Marx, _Phys. Zeitschrift_, Vol. II., p. 249; _Science Abstracts_, Vol. IV., p. 471. See also German Patent Specification No.

121,663, Cla.s.s 21a.

[50] See "The Scientific Writings of Professor Joseph Henry."

[51] _Phil. Trans._ Roy. Soc., London, 1897, Vol. CLx.x.xIX.A, p. 1.

[52] See _Proc._ Roy. Soc., London, June 12, 1902. "Note on a Magnetic Detector for Electric Waves which can be employed as a Receiver for s.p.a.ce Telegraphy," by G. Marconi.

[53] See U.S.A. Patent Specification No. 716,000, Application of July 5, 1901.

[54] See the _Electrical Review_, Vol. XLIV., 1899, May 26; _Wied Ann._, Vol. LXVIII., p. 92; or German Patent Specification No. 107,843.

[55] U.S.A. Patent Specification No. 706,742, 1902.

[56] See British Patent Specification, G. Marconi, No. 12,039, June 2, 1896.

[57] See G. Marconi, British Patent Specification No. 12,326, of June 1, 1898.