[Illustration: FIG. 51 (p. 761, _The Electrician_, Vol. XLIII.).--Apparatus for Sending and Receiving, shown by Prof. Fleming to the British Association at Dover.] A diagram of Marconi’s connection of sensitive tube to the relay and tapper-back and Morse instrument, where W represents the elevated wire, is given in Fig. 52. [Illustration: FIG. 52 (Fig. 2, of p. 691, _The Electrician_, Vol. XLII.).--Diagram of the connection of Relay and Tapper-back and Morse Instrument, as given in Mr. Marconi’s Paper in the _Journal_ of the Inst. Elec. Engineers for April, 1899; the relay being an ordinary Siemens polarised relay.] The mast at the South Foreland was stated to be 150 ft. high, but the cliff on which it stands must be at a still greater elevation above the sea. It was from this station that the real distant signalling was performed, and probably not from the lower mast at Dover. THE HISTORY OF THE COHERER PRINCIPLE. _The following, written by Dr. Oliver Lodge, appeared in_ “THE ELECTRICIAN” _for November 12th, 1897_:-- Probably the earliest discovery of cohesion under electric influence was contained in that old, forgotten observation of Guitard in 1850, that when dusty air was electrified from a point the dust particles tended to cohere into strings or flakes. The same thing no doubt occurs in the formation of snowflakes under the influence of atmospheric electrification; and the cohesion of small drops into large ones in the proximity of a charged cloud is exceedingly familiar, since it results in the ordinary thunder-shower. Great light was thrown on these meteorological phenomena by the discovery of Lord Rayleigh in 1879 of the curious behaviour of a small fountain or vertical water-jet when exposed to the neighbourhood of a stick of excited sealing-wax. A smooth orifice being arranged to throw a jet of water about three or four feet nearly vertically, the jet breaks into drops, and the drops scatter in all directions, rebounding from one another and giving a shower of fine spray; but if a stick of sealing-wax be rubbed on the sleeve of a coat and brought within one or two yards of the place where the jet breaks into drops, it will be found that the scattering ceases, the fine spray is no longer formed, and the broken jet rises and descends in great blobs of water. The rain-shower has, in fact, been converted into a thunder-shower. Further experiments, conducted chiefly with two jets, elucidated the phenomenon.[18] Arranging two nearly parallel jets from neighbouring orifices so as to impinge against each other, they were found ordinarily to rebound after colliding, a sort of film or superficial layer appearing to prevent amalgamation of the jets into one; but if a slight difference of electric potential were maintained between the two jets, say by connecting them to the terminals of a Leclanché cell, then the boundary layer broke down,--the two colliding jets no longer separated with a rebound, but amalgamated and became one.