ery
switch and siding. He knew that at night a white light displayed from the
top of a post, or swung across the track in the form of a lantern, meant
safety, a red light meant danger, and a green light meant caution. If it
had been daytime he would have seen thin wooden blades, about four feet
long by six inches wide, pivoted near the top of the same posts that now
displayed the lights. He would have learned that when these stretched out
horizontally over the track, their warning colors must be regarded by
every engineman; while if they hung down at an angle, no attention need
be paid to them.

Being a very observant boy, as well as keenly interested in everything to
be seen on a railroad, Rod soon discovered that the semaphore lights also
appeared at intervals of a few miles along the track, at places where
there were no switches, and that these always moved as soon as the train
passed them. He afterwards discovered that these guarded the ends of the
five-mile blocks, into which the road was divided along its entire length.
Each of the stations, at these points, is occupied by a telegraph operator
who, as soon as the train enters his block, displays a red danger signal
behind it. This forbids any other train to enter the block, on that track,
until he receives word from the operator at the other end of the block
that the first train has passed out of it. Then he changes his signal
from red to white, as a notice that the block is free for the admission of
the next train. This "block system," as it is called, which is now in use
on all principal railroad lines, renders travel over them very much safer
than it used to be before the system was devised.

After watching the semaphore lights for some time, and after assuring
himself that Juniper was riding comfortably, Rod spread a blanket, that
Brakeman Joe had loaned him, over a pile of loose hay, placed his M. I. P.
bag for a pillow, and in a few minutes was sleeping on this rude bed as
soundly as though he were at home.

Some hours later the long, heavily laden train stopped at the foot of the
steep grade just east of Euston, and was cut in two in order that half of
it might be drawn to the top at a time. Rear Brakeman Joe was left to
guard the part of the train that remained behind, and he did this by
walking back a few hundred yards along the track, and placing a torpedo on
top of one of the rails. Then he went back as much farther and placed two
torpedoes, one a rai