On the Fixed Signals of Railways Classic Reprint

Excerpt from On the Fixed Signals of Railways

Now that so many arms are fixed on one post, or on posts near together, it is more than ever desirable that all signal arms should at all times be distinctly in view, so as to diminish the likelihood of one being mistaken for another.

A signal is said to be on when it is at danger, and off when at caution or clear.

Although distant signals were not generally used until long after the introduction of the semaphore, disc signals continued to be put up for distant signals, and the introduction of the sema phore was for a long time limited to the junction or station signals; and hence arose a special and limited use of the word semaphore, as meaning home signal - a limited use of the word which continues to this day, even although all the signals may be of semaphore type.

Figs. 39, 40, represent the present ordinary semaphore signal, with lamp and glasses for night use. Sometimes the lamps are fitted with internal coloured glasses, movable either in a vertical or a revolving direction; but the usual plan is to have a fixed lamp, and movable external coloured spectacles. By using red and green lights only, if a coloured glass falls out the light is shown white, and thus a driver is able to warn a Signalman of the defect; whereas, if red, green, and white are used, the falling out of a red glass would not be detected, because the driver would consider the light given as white (by reason of the failure of the coloured glass) as a genuine clear signal. Fig. 41 shows the light and elegant posts of Messrs. Stevens and Sons, of lattice iron; Fig. 42, the iron posts made by the Ribbon Post Company.

In fixing signals it is frequently necessary to make them very high, in order to obtain a sky background. On the North London, where the lines are much enclosed by houses, the signal posts are sometimes upwards of 60 feet high, and it then becomes necessary to fix duplicate arms low down on the post. In Fig. 43, the high arm is seen against the sky from a distance; and as the driver approaches the post, and the high arm is less distinguish able, the lower arm becomes more so. The two arms, and of course the glasses of the lights also, are moved together by the same mechanism.

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