In these days, when our ocean highways and harbours are crowded with shipping, a collision between two of our large iron or steel vessels, which might happen at any time, would send one of them to the bottom in a few minutes. Two vessels, each going at a speed of twenty miles an hour, and sighting one another at two miles off, with this joint speed of forty miles an hour, would meet in about three minutes. Hence the importance of a ready and efficient method of signalling. By the present system, red and green lights are placed on each side of the vessel, a green light on the starboard side, and a red light on the port side, with a board shutting off each light from the opposite side. An officer seeing a coloured light at a distance of two miles has no indication what course the vessel is steering. Hence the importance of the apparatus invented by The Right Hon. J. H. A. Macdonald, Q.C., M.P., Edinburgh, an Associate of the Society of Telegraph Engineers and Electricians, which he calls the Electric Holophote Course-indicator, for the prevention of collisions at sea. By means of a powerful electric light, the approach of another vessel is indicated, and information is given at the same time as to what course she is on and what course she intends to hold to. The light is also useful for illuminating the water immediately before the ship, and is also valuable when passing down a river, through shoals, or close to a lee shore. The instrument consists of a strong reflector, with an arc light placed in the middle of it, which is affected by every movement of the helm. As long as the helm is amidships, the handle cannot be moved at all, but is held firm by two pegs. But if the helm is moved from amidships, an electric circuit is formed, which actuates an electro-magnet, and thereby removes one of the pegs. When the helm is ported, the reflector is set free by the removal of one of the pegs, so that by working the handle, the light can be swept from amidships over the starboard bow, and brought back again. If the helm be starboarded, the reflector is freed from the other peg, so that the light can be swept from amidships over the port bow and back again. But as this is a mere side-to-side movement, means are provided for giving more intelligible information, such as a driver gives when waving his hand to indicate his course, by a shutter connected with the reflector in such a way that when the beam has completed its side-movement, the shutter rises up and obscures the light, and does not drop again until the reflector has been turned back to its middle position. The shutter then falls down; and the light being again exposed, the process of sweeping round to starboard, screening, and bringing back to amidships, can be repeated as long as the helm remains at port. When the helm is starboarded, the light can be swept round to port in the same way. The light is immovable when the helm is amidships, and can be swept only