ions,--the fundamental law of telegraph-working being, that
two engines are not to be allowed to run on the same line between two
signal-stations at the same time.

When a train passes one of such stations, it is immediately signalled
on--usually by electric signal-bells--to the station in advance, and that
interval of railway is "blocked" until the signal has been received from
the station in advance that the train has passed it. Thus an interval of
space is always secured between trains following each other, which are
thereby alike protected before and behind. And thus, when a train starts
on a journey, it may be of hundreds of miles, it is signalled on from
station to station--it "lives along the line,"--until at length it
reaches its destination and the last signal of "train in" is given. By
this means an immense number of trains can be worked with regularity and
safety. On the South-Eastern Railway, where the system has been brought
to a state of high efficiency, it is no unusual thing during Easter week
to send 600,000 passengers through the London Bridge Station alone; and
on some days as many as 1200 trains a-day.

While such are the expedients adopted to ensure safety, others equally
ingenious are adopted to ensure speed. In the case of express and mail
trains, the frequent stopping of the engines to take in a fresh supply of
water occasions a considerable loss of time on a long journey, each
stoppage for this purpose occupying from ten to fifteen minutes. To
avoid such stoppages, larger tenders have been provided, capable of
carrying as much as 2000 gallons of water each. But as a considerable
time is occupied in filling these, a plan has been contrived by Mr.
Ramsbottom, the Locomotive Engineer of the London and North-Western
Railway, by which the engines are made to _feed themselves_ while running
at full speed! The plan is as follows:--An open trough, about 440 feet
long, is laid longitudinally between the rails. Into this trough, which
is filled with water, a dip-pipe or scoop attached to the bottom of the
tender of the running train is lowered; and, at a speed of 50 miles an
hour, as much as 1070 gallons of water are scooped up in the course of a
few minutes. The first of such troughs was laid down between Chester and
Holyhead, to enable the Express Mail to run the distance of 841 miles in
two hours and five minutes without stopping; and similar troughs have
since been laid down at Bushey near L