[1] See Lodge and Howard, Philosophical Magazine for July, 1889. See also Phil. Mag., August, 1888, page 229.

[2] Cf. sections 157A, 143, 187, and chap. xvi., of my Modern Views of Electricity.

[3] Radian is the name given by Prof. James Thomson to a unit angle of circular measure, an angle whose arc equals its radius, or about 57°.

[4] The word "stationary" is ambiguous. I propose to use "stagnant," as meaning stationary with respect to the earth, i.e. as opposed to stationary in space.

[5] Lord Rayleigh, Nature, March 25, 1892.

[6] It does not seem to have been noticed that in Query 22, quoted in the Introduction to the present book, Newton seems to throw out a curious hint in this same direction,—though he immediately abandons it again. He does not appear to have carefully edited his queries; probably they were published posthumously.

[7] On doing the arithmetic, however, I find the necessary concentration absurdly great, showing that such a mass is quite insufficient. (See Appendix 1.)

[8] See Lodge, Philosophical Magazine, April, 1907. Also Appendix 2 below.

[9] Address to Section A of British Association at Montreal, 1884.

[10] Philosophical Magazine, Dec., 1887.

[11] Archives NÉerlandaises (1869), Vol. IV, p. 443, or Nature, Vol XXVI, p. 500. Also Chapter IV above.