Major-General Pasley, in a pamphlet published in 1823, entitled Description of the Universal Telegraph for Day and Night Signals,' abandons the polygrammatic principle, and adopts the simple form shown In fig. 8, which represents what he 'styles the " universal tele graph," as adapted for day-service. It consists of an upright poet with two arms, both attached to one pivot at its upper extremity. Each arm is capable of assuming the seven positions indicated in the cut, besides what is called the stop, which is made when turned down and obscured by the post. Twenty-eight distinct signals may therefore be made by the apparatus, as shown in the subjoined table ; these being more than sufficient for the letters of the alphabet, though not numerous enough to allow of a full alphabet and the numeral characters.
It had been found, in using Sir Homo Popham's ship-semaphores that uncertainty was occasioned by the signals being sometimes seen in reverse, in which case one number or eigu would be confounded with another ; Pasley provided against this occurrence with his universal telegraph by the addition of the auxiliary arm, or indicator, marked a, fig. 8, which, in whatever direction the machine may be viewed, distin guishes the side at which the numeral signs commence. It serves also to prevent the position marked 4 from being confounded with the stop, which it might be if there were nothing to indicate that the telegraph is at work, and to enable the eye to measure its height. The counter balance weights of the arms are not fixed close to the pivot, but extend to some distance from it, in the form of a slender framework of iron, with a ball at the outer extremity, their light appearance rendering them almost invisible at a distance. Pasley states that telegraphs should in general be painted black, and, if possible, so placed that they may be seen without any background. If, however, a background be unavoidable, the telegragh should be of such a colour as to contrast with it. In some eases, where the appearance of the background varies much at different periods of the day, it has been found useful to paint the arms white and black, in large chequers, each occupying half of the width and half of the length of the arm.
The contrivances which have been suggested for effecting telegra phic communication are so very numerous, that anything like an enume ration of them is impossible in this place. Several depend upon the application of arms of various forms to a semaphoric telegraph, while another class of telegraphic contrivances depend upon the exhibition of devices or symbols, in a manner somewhat resembling the original contrivance of Dr. Hooke. In Mr. Spencer's anthropo-telegraph; a man holds a couple of discs in his hands, and makes signals by placing them in different positions with respect to each other. But the reader, interested in this sort of detail, which is now purely historical, may gratify his curiosity by referring to the Transactions of the Society of Arts.' 31acdonald'e Treatise on Telegraph Communication' (1817), also contains a multitude of similar details.
Marine telegraphic communication is en object of great importance, since there are many circumstances which render personal communica tion between vessels at sea impracticable, and that sometimes in cases of the greatest emergency. But, although naval signals have been, of necessity, long used, and flags of various forms and colours have been extensively employed for the purpose of making them, it was not till within a comparatively recent period that they were reduced to anything like an efficient telegraphic system. $ir John Barrow states (• Ency. Brit., art. ' Navy ') that " The idea of numbering the flags, and of assigning a certain number of corresponding sentences to certain combinations of these numbers, was reduced to something approaching a regular system in the fleet of Lord Howe;" and that in the year 1798 a new signal-book was issued by the Admiralty, the references to which were made by a numerical arrangement of flags. This book contained about four hundred sentences, expressive of the most usual operations of the fleet ; but it was so imperfect that, if any order had to be transmitted which was not to be found in the dictionary, it became neeesaary to make the signal for "a boat from each ship ;" an order which could not always be complied with. This inconvenience was remedied by the plan, suggested by Sir Home Popham, of making the flag-signaht represent the letters of the alphabet, as well as words and sentences, in connection with numbers. He also printed, at Calcutta, a new code of naval signals, which was subsequently re printed in England, greatly extended, and adopted for use in the navy. Among the numerous improvements introduced by him is a new method of cutting the signal flags, so that, as he explained to the Society of Arts in 1816, " the selvages of the buntin are brought on the outer edges of the flags, and the gorings in the centre; by which means the outer edge is susceptible of the least air of wind, and when the flag blows out, the gorings assist in keeping it out; whereas the old flags had a hem on the outside, which rendered them difficult to be moved without a fresh breeze, especially in damp and rainy weather, as the hem then became very heavy." "Besides," ho adds, "it is impossible, from the nature of the buntin, to sew a straight seam, for the instant it is cut it will become in some degree curved." (' Trans actions,' vol. xxxiv.) The principle of the numerical system as applied to flag-telegrapha in the navy is briefly explained by 31aedonald. Nine dillerent varie gated flags are employed to express the numerals 1 to 9, another for 0, and another called a substitute, to repeat any flag under which it is hoisted, in the case of the same numeral occurring twice in the number ts be expressed. A pendant is also used in some cases as a substitute for the uppermost figure ; and thus, by the use of eleven different flap and a pendant, any number from 1 to 999 may be expressed without displaying more than three flags, or two flags and a pendant, at once.