RAILWAY TRAVELLING AND ELECTRICITY. 
143 
of the railway engineer. Thus, at every railway station, level 
crossing, or junction, signal-posts are erected which convey to 
the approaching engine-driver — by exposing discs, bars, or sema- 
phore arms in different positions by day, or lamps displaying 
different colours by night — the fact that the line is clear for him 
to proceed or obstructed so that he must stop. The favourite 
signal by day — the survival of the fittest — is the arm, which, 
when at right angles, implies danger , and when at an angle of 
45°, safety , and 
White means right : red means wrong : 
Green means slowly go along, 
teaches the young railway lad the rule of the road by night. 
The character of every train is indicated by its head lights , and 
its presence to an approaching train by its tail lamps. Should 
thick weather prevent the sight of the signals, detonating fog 
.signals announce the contiguity of danger. The marshalling 
of trains in station yards and platforms are produced by whistles 
and flags by day and lamps by night, all forming a species of 
telegraphic language between the fixed station and the moving 
train. 
Where telegraphy is required to reach distances beyond the 
sphere of the ear or the eye, electricity is employed, and the 
electric telegraph becomes of prime and essential use, not only 
in regulating the traffic on double and single lines, but in 
securing safety. Special trains are moved about by its means, 
delays are remedied, breaksdown rendered harmless, runaway 
engines have been overtaken by its aid, passengers’ luggage 
recovered ; but, above all, irregularities are by its means rapidly 
announced, and the evils of unpunctuality rendered innocuous. 
The greatest element of safety on railways is, however, the 
Block System. 
The block system arose out of the multiplication of trains, 
and the necessity for increased speed. Necessity, the mother of 
invention, brought it into existence. 
By it trains travelling upon the same line of rails are kept 
apart by a certain and invariable interval of space , instead of 
by an uncertain and variable interval of time . 
The practice under the “time ” system is to exhibit the danger 
signal for five minutes, and the caution signal for five minutes 
more, after a train or engine has been despatched from or past 
any station, junction, level crossing, or siding. Trains are 
thus said to be kept apart by fixed periods of five minutes, and 
if the caution signals were properly regarded, by an interval of 
time even longer than that. The safety of the train is entirely 
the responsibility of the driver. Immunity from accident is 
dependent upon his keeping a clear look-out. If engines ran 
