The invention is also applicable to lightships, many of which are manned by four men or more at a large cost per annum. In the majority of cases an unattended Stevenson lightship--such as described in another chapter, six of which are in use around the coasts of Scotland, and which give, not only a first-class light, but, by the aid of the fog-signal gun, can be made to give an excellent fog-signal as well--offers a means of reducing the heavy maintenance charges arising in connection with a manned light-vessel. In many instances existing lightships can be converted to the automatic system and completed by the gun. Each case must, of course, be decided upon its merits as regards the time the gun and light are required to work upon a single charge of acetylene, but there are no insuperable obstacles to its utilization. Of course, in an isolated station lying perhaps some miles off the mainland, it may be necessary to keep the gun going night and day in fog and in clear weather alike. In this case, naturally, the great number of explosions involves considerable expense; but the inventors are carrying out experiments with a view to switching the gun on and off, as required, from a distant point by means of wireless telegraphy, so as to effect a saving in the expenditure of acetylene when there is no need on account of fine weather to keep the gun going. Still, it must not be supposed that the detonations even during clear weather are altogether abortive, inasmuch as a sound-signal at sea, where the atmosphere has a long-distance-carrying capacity as a rule, in conjunction with a light, draws double attention to a danger spot. Under such circumstances the waste of acetylene gas during periods of clear weather is more apparent than real. The contest against the elements is still being waged, and slowly but surely engineering science is improving its position, and is hopeful of rendering audible signals as completely effective as those of a visual character. CHAPTER V THE EDDYSTONE LIGHTHOUSE It is doubtful whether the name of any lighthouse is so familiar throughout the English-speaking world as the “Eddystone.” Certainly no other “pillar of fire by night, of cloud by day,” can offer so romantic a story of dogged engineering perseverance, of heartrending disappointments, disaster, blasted hopes, and brilliant success.