Communication between the vessels of the fleet is effected at night by means of the flashing light worked on the short and long flash principle, invented by Captain Colomb, R.N. There are few sights more suggestive of the advance in modes of communication and the development of the inventive faculty than that of the admiral ‘talking’ to his captains by means of the flashing lamp in the darkness of the night and far out on the trackless ocean. It may be necessary during the night to alter the course of the squadron. If the course indicated at sunset be due north, and it be required to alter the direction to west, all lights on board the flagship, except the flashing light, are carefully obscured, and the brilliant rays of a solitary lamp leap through the darkness conveying the order, ‘Alter course to west.’ The instructions contained in the General Signal Book are varied and comprehensive. Upwards of a thousand separate signals, adapted to every probable change of condition and circumstance in times of peace and in the exigences of battle, are concisely set forth, every tactical order being elucidated by diagrams showing the direction to be taken and the position to be assumed by each ship. The Vocabulary Signal Book, as its name indicates, is a sort of dictionary, but possessing also the character of a lexicon, as not only words in alphabetical order, but phrases under their proper heading, are methodically arranged in its pages. For example, under the heading of ‘Admiral,’ which word is represented in ‘flag language’ by A.H.V., will be found, ‘Admiral desires,’ ‘Admiral intends,’ and the cheerful announcement, ‘Admiral requests the pleasure of your company to dinner.’