In 1885 Sir William Preece, now consulting electrical engineer to the General Post-Office, erected near Newcastle two insulated squares of wire, each side 440 yards long. The squares were horizontal, parallel, and a quarter of a mile apart. On currents being sent through the one, currents were detected in the other by means of a telephone, which remained active even when the squares were separated by 1000 yards. Sir William Preece thus demonstrated that signals could be sent without even an earth connection, _i.e._ entirely through the ether. In 1886 he sent signals between two parallel telegraph wires 4-1/2 miles apart. And in 1892 established a regular communication between Flatholm, an island fort in the Bristol Channel, and Lavernock, a point on the Welsh coast 3-1/3 miles distant. The inductive method might have attained to greater successes had not a formidable rival appeared in the Hertzian waves. In 1887 Professor Hertz discovered that if the discharge from a Leyden jar were passed through wires containing an air-gap across which the discharge had to pass, sparks would also pass across a gap in an almost complete circle or square of wire held at some distance from the jar. This “electric eye,” or detector, could have its gap so regulated by means of a screw that at a certain width its effect would be most pronounced, under which condition the detector, or receiver, was “in tune” with the exciter, or transmitter. Hertz thus established three great facts, that-- (_a_) A discharge of static (_i.e._ collected) electricity across an air-gap produced strong electric waves in the ether on all sides. (_b_) That these waves could be _caught_. (_c_) That under certain conditions the catcher worked most effectively. Out of these three discoveries has sprung the latest phase of wireless telegraphy, as exploited by Signor Marconi. He, in common with Professors Branly of Paris, Popoff of Cronstadt, and Slaby of Charlottenburg, besides many others, have devoted their attention to the production of improved means of sending and receiving the Hertzian waves. Their experiments have shown that two things are required in wireless telegraphy-- (i.) That the waves shall have great penetrating power, so as to pierce any obstacle. (ii.) That they shall retain their energy, so that a _maximum_ of their original force shall reach the receiver. The first condition is fulfilled best by waves of great length; the second by those which, like light, are of greatest frequency. For best telegraphic results a compromise must be effected between these extremes, neither the thousand-mile long waves of an alternating dynamo nor the light waves of many thousands to an inch being of use. The Hertzian waves are estimated to be 230,000,000 per second; at which rate they would be 1-1/2 yards long. They vary considerably, however, on both sides of this rate and dimension.