But in two respects especially has electricity within the last few years shown itself to be of the greatest service to the ship at sea. Taking them in the reverse order of their chronology, there is first of all the system of submarine signalling so recently installed. This takes advantage of the fact that water is a conductor of sound, and with a speed more than four times quicker than air. In the case of fog overtaking a steamer approaching land, or the vicinity of a channel marked by buoys or lightships, it is possible to obtain warning by sound when sight is denied, and this at a distance of four or five miles. The submarine bell is attached to buoy or lightship, whilst the receiving apparatus is attached to the interior of the ship’s hull at the bows. From there the signals are conveyed to the chart-house by means of telephones. One receiver is placed on each bow inside the plating of the ship between the keel and the water-line, so that the bell may be located on either side. A very interesting instance of the utility of submarine signalling was afforded recently in the case of the _Kaiser Wilhelm II._, which, owing to a dense fog, was anchored off Cherbourg. Her tender was awaiting her just outside the harbour, and sounded her submarine bell to indicate the direction to be steered in order that the big liner might make port. At a distance of no less than fifteen miles away the _Kaiser Wilhelm II._ picked up the signals by her receivers, and was enabled to find her way into the French harbour by this means alone.