Some dynamo machines are coupled direct to the crank shaft of the steam engines; they require the same kind of attention as others, that is to say, they should be driven at a uniform speed, should be well oiled as well as the steam-engine, and they should be kept clean and free from sharp grit. _Application._--The electric light used in the case of a _direct_ attack by torpedo boats, without the assistance of guard boats, will not prove of much assistance, on account of the very small space covered by the beam of light, and therefore if the direction of attack is not exactly known, the beam of light must be kept continually sweeping round the horizon on the chance of picking out the attacking boats, and thus, while flashing in one direction, they may be approaching in another, and effect their deadly mission. Every man-of-war should be fitted with at least three electric lights, whereby the above-mentioned want of space covered would be to a considerable degree obviated. If a powerful beam of light be thrown in a particular direction, and there kept stationary, all boats or vessels crossing its path at a distance not exceeding 1600 yards from the ship using the electric light, would become distinctly visible to observers placed behind the light; these vessels remaining visible as long as they continue in such a position that the beam of light acts as a background to them. Under very favourable circumstances, the distance at which the above effect may be observed is much increased. The parabolic reflector extends only about an arc of 33° at 540 yards' distance from the light. One defect of this form of reflector is, that it is rapidly dimmed by spray, rain, and by the particles given off by the carbons. The catadioptric lens, or holophote, gives a far more powerful but a more concentrated beam than the parabolic reflector. By means of such a beam of light, a torpedo boat may be discerned at about one mile distance. By adding divergent lens to the holophote, a less powerful and less concentrated beam of light will be thrown out; in this case about 20° of surrounding water would be well illuminated at about 900 yards' distance, while without the divergent lens there would be only about 5° so illuminated but far more brilliantly. The distance at which objects can be detected by the electric light depends on their size and _colour_, more particularly on the latter. The observer should as a rule be well removed from the light. In the case of an electric light being thrown on the observer, the vessel, &c., using it would to that observer be invisible, the light only being seen; also when directed on any particular object, surrounding objects would be thrown into shade.