Since the first edition of this work was published, an occulting light has been exhibited for about three weeks, representing during each night the constant repetition of one of the following numbers, 136, 227, 354, 432. As might easily have been anticipated, its effect was quite satisfactory in determining those numbers. At about a distance of a quarter of a mile, its occultations were even more distinct than at shorter distances. Successive improvements have occurred, until it now seems desirable to revise and simplify the light-houses of the world, by making them speak one universal language, intelligible even to the commonest capacity. No time could be more favourable than the present for establishing an international system of signals, founded on numbers, and adapted to the wants and convenience of all nations. The following brief outline of such a plan requires, therefore, no apology. The present modes of identifying lighthouses are by 1. The _colour_ of the lights. 2. The _number_, _distance_, and _relative position_ of the lights exhibited. 3. The _variations_ in colour or intensity, or in the time during which the lights are partially or totally obscured, compared with that during which they are visible. 4. By striking bells or gongs in foggy weather. There are around the coasts of Great Britain about 290 light-houses and light-ships. They exhibit nearly 390 lights. Of these, about one hundred lights are coloured, chiefly red. Fifty-five are revolving lights, varying in their periods from five seconds to four minutes. In foggy weather fifteen of these toll bells, and thirty-three strike gongs. It is proposed to abolish all the revolving lights, and to retain white light, to distinguish by its occupations the number of the light-house which it is destined to indicate. With respect to those lighthouses which indicate ports, next to the information as to the name of the port, the most important question is the depth of water at its entrance. This may be given by allowing the occupations of the white light to indicate the number of the port, after which a glass of green or of any other colour being interposed, the number of occultations mark the number of feet of the depth of water at the time. A float in a well, to which the tide has access by a small aperture, will serve the double purpose of raising the weight that drives the mechanism for occulting, and of prescribing, according to the height of the tide in feet, the corresponding number of occultations of the green light. Thus a constant alternation will go on during the whole night of repetitions of the _number_ of the port, by occultations of white light, and of the number of feet which indicate the depth of water at its entrance, by green light.