[1] This series of articles is based on the Cantor Lectures delivered before the Society of Arts, London, in March, 1903. The lectures were attended by many of the leading British scientific men and electrical engineers, and attracted wide attention as the most complete and authoritative statement hitherto made of wireless telegraphy. In writing the articles for the "Popular Science Monthly," the author has omitted advanced technicalities in order that the substance may be suitable for the general reader.—Editor.

[2] For a more detailed account of this hypothesis, the reader is referred to an article by the present writer, entitled "The Electronic Theory of Electricity," published in the "Popular Science Monthly" for May, 1902.

[3] See J. J. Thomson, "Recent Researches in Electricity and Magnetism," chap. I., p. 16.

[4] See O. Heaviside, "Electromagnetic Theory," Vol. I., p. 54.

[5] Wiedemann's Annalen, 36, p. 1, 1889; or in his republished Papers, "Electric Waves," p. 137, English translation by D. E. Jones.

[6] The fraction 7/22 here denotes a stranded wire formed of seven strands, each single wire having a diameter expressed by the number 22 on the British standard wire gauge.

[7] G. Marconi, "Syntonic Wireless Telegraphy," Journal of the Society of Arts, Vol. XLIX., p. 501, 1901.

[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."

[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 0·5 million to 1·6 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 Lumière 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. XXXII., 1893, p. 123. See also Professor Minchin, Phil Mag., January, 1894, Vol. XXXVII., 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 title 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 title 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. CXXXIV., 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, Class 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. CXXX., 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 Institution, 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, Class 21a.

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

[51] Phil. Trans. Roy. Soc., London, 1897, Vol. CLXXXIX.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 Space 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.

[58] See the Electrical Review, September 26, 1902, Vol. LI., p. 543.

[59] There is a good deal of contradiction between various inventors on this point, some saying that "earthed" aerials obviate atmospheric electrical disturbances, and others that insulated aerials are in this respect superior. The truth appears to be that, neither form is absolutely free from risk of disturbance by this cause.

[60] The capacity of an electrical circuit corresponds to the elastic pliability, or what is commonly called the elasticity, of a material substance, and the inductance to mass or inertia. Hence capacity and inductance are qualities of an electric circuit which are analogous to the elasticity and inertia of such a body as a heavy spring.

[61] See Cantor Lectures, on "Electrical Oscillations and Electric Waves," delivered before the Society of Arts, London, November 26, December 4, 10, 17, 1900. Lecture I., p. 12, of reprint.

[62] A fuller account of these experiments was given by the author in a letter to the London Times published on April 14, 1903.

[63] See Journal of the Society of Arts, Vol. XLIX., p. 505. "Syntonic Wireless Telegraphy," by G. Marconi.

[64] See German Patent Specifications, Class 21a, No. 7,452 of 1900, and also No. 8,087 of 1901.

[65] See German Patent Specification, Class 21a, No. 7,498 of 1900, applied for November 9, 1900. The above-mentioned patent is subsequent in date to Mr. Marconi's experiments on the same subject.

[66] See The Electrician, January 18, 1900, Vol. XLVI., p. 475. Also reprint of a Paper of Professor A. Slaby, "Abgestimmte und mehrfache Funkentelegraphie."

[67] See British Specification No. 11,348 of 1901.

[68] See Comptes Rendus, May 21, 1900; Rapports du Congrès International d'Electricité, Paris, 1900, p. 341.

[69] See The Electrician, Vol. XLVI., p. 573, February 8, 1901.

[70] See The Electrician, Vol. L., p. 418, January 2, 1903.

[71] See Mr. Marconi's Friday evening discourse at the Royal Institution, June 13, 1902; also The Electrician, Vol. XLIX., p. 390.

[72] See Proc. Roy. Soc., June 12, 1902. "A Note on the Effect of Daylight upon the Propagation of Electromagnetic Impulses over Long Distances," by G. Marconi.

[73] See Phil. Mag., Vol. IV., p. 253, Series 6, August, 1902. J. J. Thomson, "On Some Consequences of the Emission of Negatively-electrified Corpuscles by Hot Bodies."

[74] The opinion that ionisation of the air by sunlight is a cause of obstruction to Hertzian waves propagated over long distances has also been expressed by Mr. J. E. Taylor. See Proc. Roy. Soc., Vol. LXXI., p. 225, 1903. "Characteristics of Earth Current Disturbances and their Origin."

[75] See Proc. Roy. Soc., May 15, 1902. "On Some Phenomena affecting the Transmission of Electric Waves over the Surface of the Sea and Earth," by Captain H. B. Jackson, R.N., F.R.S.

[76] Mr. Marconi has informed the writer that these strategic questions have received attention in selecting the sites for large Marconi power stations in Italy.