of boats where the river
ceased to be navigable; for it was then necessary to employ a great
number of negroes for carrying both the boats and the luggage. The
explorers were, more or less, left to the mercy of the natives, and but
very slow progress could be made.

On returning from one of these expeditions in Africa, Dr. Balay and M.
Mizon conceived the idea of applying to M. Decauville for advice as to
whether the narrow-gauge line might not be profitably adapted for the
expedition. M. Decauville proposed to them to transport their boats
without taking them to pieces, or unloading them, by placing them on two
pivot trollies, in the same manner as the guns are transported in
fortifications and in the field. The first experiments were made at
Petit-Bourg with a pleasure yacht. The hull, weighing 4 tons, was placed
on two gun trollies, and was moved about easily across country by means
of a portable line of 20 in. gauge, with 14 lb. rails. The length of the
hull was about 45 ft., depth 6 ft. 7 in., and breadth of beam 8 ft. 2
in., that is to say, five times the width of the narrow-gauge, and
notwithstanding all this the wheels never came off the line. The
sections of line were taken up and replaced as the boat advanced, and a
speed of 1,100 yards per hour was attained. Dr. Balay and M. Mizon
declared that the result obtained exceeded by far their most sanguine
hopes, because during their last voyage, the passage of the rapids had
sometimes required a whole week for 1,100 yards (1 kilometer), and they
considered themselves very lucky indeed if they could attain a speed of
one kilometer per day. The same narrow gauge system has since been three
times adopted by African explorers, on which occasions it was found that
the 20 in. line, with 9 lb. or 14 lb. rails, was the most suitable for
scientific expeditions of this nature.

The trucks used are of the kind usually employed for military purposes,
with wheels, axles, and pivot bearings of steel; on being dismounted the
bodies of the two trucks form a chest, which is bolted together and
contains the wheels, axles, and other accessories. The total weight of
the 135 yards of road used by Dr. Balay and M. Mizon during their first
voyage was 2,900 lb., and the wagons weighed 5,000 lb. Hence the
expedition had to carry a supplementary weight of 31/2 tons; but at any
given moment the material forming this burden became the means of
transporting, in its turn, seven boats, represe