In the present development of railroad signalling the banner and disc patterns have a comparatively limited application, although, on the whole, they are largely used. The banner signal is mostly employed in the manual operation of switches, turn-outs, and cross-overs, and for other local purposes, particularly on lines of light traffic. [Illustration: FIG. 10.—Semaphore Signals.] =271. The Semaphore.=—The semaphore is now mainly used in connection with block signalling. Like many other appliances in railroad signalling it was first used in England, by Mr. C. H. Gregory, about 1841. Its name is derived from the combination of two Greek words signifying a sign-bearer. It consists of a post varying in height from about 3 to 35 or 40 feet, carrying an arm at its top from 3 to 5 feet long, pivoted within a foot or 18 inches of one end, the long end suitably shaped and painted and the other arranged with a lens so that when operated at night in connection with a lamp it may exhibit a properly colored light. The post of the semaphore is placed alongside the track so as to be on the right-hand side of an approaching train, the long arm rising and falling as a signal away from the track and in a plane at right angles to it. The other arm of the semaphore signal may be connected by wires or rods and light chains running over pulleys with suitable levers and weights operated either in a near-by signal cabin or by a signalman stationed near the semaphore itself; or it may be operated by electric or pneumatic power, as in many of the later installations. The semaphore may, therefore, be operated at the post or by suitable appliances at a distance. [Illustration: Semaphore on Pennsylvania Railroad.] =272. Colors for Signalling.=—The colors used either for painted signals for daylight exposure or for coloring lenses for night signalling are red, white, and green, as ordinarily employed in this country; red signifying “danger” or “stop,” white signifying “safety” or “clear track,” and green signifying “caution” or “proceed with train under control,” indicating that a train may go forward cautiously, expecting to find an obstruction or occupied track. In England green is largely employed to indicate “safety” or “clear track,” on the ground that a white light is so similar to any other in its vicinity that the latter may too easily be mistaken for a signal. While there is some diversity of views in this country on that point, the consensus of engineering opinion seems to favor the retention of the white for the track safety signal.