[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.