, at a rate of nearly 3 m.
an hour. On the Aire and Calder navigation, where the locks have a
minimum length of 215 ft., a large coal traffic is carried in trains of
boat-compartments on a system designed by W.H. Bartholomew. The boats
are nearly square in shape, except the leading one which has an ordinary
bow; they are coupled together by knuckle-joints fitted into hollow
stern-posts, so that they can move both laterally and vertically, and a
wire rope in tension on each side enables the train to be steered. No
boat crews are required, the crew of the steamer regulating the train.
If the number of boats does not exceed 11 they can be pushed, but beyond
that number they are towed. Each compartment carries 35 tons, and the
total weight in a train varies from 700 to 900 tons. On the arrival of a
train at Goole the boats are detached and are taken over submerged
cradles under hydraulic hoists which lift the boat with the cradle
sufficiently high to enable it to be turned over and discharge the whole
cargo at once into a shoot and thence into sea-going steamers. Another
method of utilizing steam-power, which was also first tried on the Forth
and Clyde canal by Symington in 1789, is to provide each vessel with a
separate steam engine, and many barges are now running fitted in this
way. Experiments have also been made with internal combustion engines in
place of steam engines. In some cases, chiefly on rivers having a strong
current, recourse has been had to a submerged chain passed round a drum
on a tug: this drum is rotated by steam power and thus the tug is hauled
up against the current. To obviate the inconvenience of passing several
turns of the chain round the drum in order to get sufficient grip, the
plan was introduced on the Seine and Oise in 1893 of passing the chain
round a pulley which could be magnetized at will, the necessary
adhesion being thus obtained by the magnetic attraction exercised on
the iron chain; and it was also adopted about the same time in
combination with electrical haulage on a small portion of the Bourgogne
canal, electricity being employed to drive the motor that worked the
pulley. Small locomotives running on rails along the towpath were tried
on the Shropshire Union canal, where they were abandoned on account of
practical difficulties in working, and also on certain canals in France
and Germany, where, however, the financial results were not
satisfactory. On portions of the Teltow canal, joi