[Illustration: Fig. 74--Wehnelt interrupter] It is singular how discoveries sometimes arrive abreast of each other so as to render mutual aid, or supply a pressing want almost as soon as it is felt. The coherer in its present form is actuated by waves of comparatively low frequency, which rise from zero to full height in extremely brief periods, and are separated by periods decidedly longer (Fig. 73). What is needed is a plan by which the waves may flow either continuously or so near together that they may lend themselves to attuning. Dr. Wehnelt, by an extraordinary discovery, may, in all likelihood, provide the lacking device in the form of his interrupter, which breaks an electric circuit as often as two thousand times a second. The means for this amazing performance are simplicity itself (Fig. 74). A jar, _a_, containing a solution of sulphuric acid has two electrodes immersed in it; one of them is a lead plate of large surface, _b_; the other is a small platinum wire which protrudes from a glass tube, _d_. A current passing through the cell between the two metals at _c_ is interrupted, in ordinary cases five hundred times a second, and in extreme cases four times as often, by bubbles of gas given off from the wire instant by instant. FOOTNOTES: [3] "History of the Wireless Telegraph," by J. J. Fahie. Edinburgh and London, William Blackwood & Sons; New York, Dodd, Mead & Co., 1899. This work is full of interesting detail, well illustrated. [4] The value of wireless telegraphy in relation to disasters at sea was proved in a remarkable way yesterday morning. While the Channel was enveloped in a dense fog, which had lasted throughout the greater part of the night, the East Goodwin Lightship had a very narrow escape from sinking at her moorings by being run into by the steamship _R. F. Matthews_, 1,964 tons gross burden, of London, outward bound from the Thames. The East Goodwin Lightship is one of four such vessels marking the Goodwin Sands, and, curiously enough, it happens to be the one ship which has been fitted out with Signor Marconi's installation for wireless telegraphy. The vessel was moored about twelve miles to the northeast of the South Foreland Lighthouse (where there is another wireless-telegraphy installation), and she is about ten miles from the shore, being directly opposite Deal. The information regarding the collision was at once communicated by wireless telegraphy from the disabled lightship to the South Foreland Lighthouse, where Mr. Bullock, assistant to Signor Marconi, received the following message: "We have just been run into by the steamer _R. F. Matthews_ of London. Steamship is standing by us. Our bows very badly damaged." Mr. Bullock immediately forwarded this information to the Trinity House authorities at Ramsgate.--_Times_, April 29, 1899. ELECTRICITY, WHAT ITS MASTERY MEANS: WITH A REVIEW AND A PROSPECT GEORGE ILES