438
EXPOSITION AT VIENNA.
Inspecteur, etc.), railway signals were divided into four classes, as follows: —
1. For the "covering” of trains (i. e., to indicate by optical signals that a train has passed a signal-station and that another must not follow).
2. To signal the movement of trains (electrically).
3. To signal from trains in case of accident.
4. To communicate between the various portions of a train.
Having in view, however, the prime object of the signal- service, a more logical division of the subject would seem to be one based on the actual course of trains from station to station and the character of accidents to which they are liable.
Aside from those arising from the imperfect condition of the track or rolling stock of a railway, which can only be avoided by frequent inspection, the dangers to which trains are subject are principally occasioned by —
1. The displacement of switches or semaphores at stations.
2. Vehicles, etc., upon the track at common road-crossings.
3. Collision of trains in motion, following or meeting each other, on the same track or at junctions.
4. Causes within the train itself.
The signals themselves cannot be so readily classified as the dangers which they are intended to avert, inasmuch as some of the apparatus may be used with equal facility to attain several of the objects desired. For the purposes of this report, however, it will be sufficient if I explain their actual uses, merely suggesting others to which they may be applied.
From this stand-point (i. e., of the purposes they are designed to serve,) railway signals may be considered in six groups, viz. : —
1. Signals of the movement of trains.
2. Signals giving knowledge of or control over the position of switches or semaphores not visible to the person requiring such knowledge or control.