or the most part, explorers must drive their own beasts
with them: they must see to their being watered, tended, and run after
when astray; help to pack and harness them; fatigue themselves for their
benefit; and drudge at the work of a cowherd for some hours a day.

In fitting out a caravan, as few different kinds of animals should be
taken as possible, or they will split into separate herds, and require
many men to look after them.

The dispositions of the animals that compose a caravan affect, in no
small degree, the pleasure of travelling with it. Now, it is to be
noticed that men attach themselves to horses and asses, and in a lesser
degree to mules and oxen, but they rarely make friends of camels.

Weights carried by Cattle.--The net weights that these different animals
carry in trying, long-continued journeys--through stages uncertain in
length, sometimes leading to good pasture, sometimes to bad--must not be
reckoned higher than the following; and an animal draws about 2 1/2 times
as much net weight as he carries:--An ass, 65 lbs.; a small mule, 90
lbs.; a horse lbs.; an ox lbs.; a camel lbs. to 200 lbs.;
elephant lbs. In level countries--where there is grain, and where
the road is known and a regularity in the day's work can be ensured--the
weights that may be carried are fully double those of the above list.
Captain Burton's donkeys, in East Africa, carried immense weights. Dogs
will draw a "travail" (which see) of 60 lbs. for a distance of 15 miles a
day, upon hard level country.

Theory of Loads and Distances.--How should we load men or animals of
transport, and how should we urge them, in order to obtain the largest
amount of effective labour? If they carry a mere feather-weight, they may
make long days' journeys; but their value, as animals of transport, is
almost nothing. Again, on the other hand, if we load them with an
excessive weight, they will soon come to a standstill; and in this case,
as in the first, their value as beasts of transport is almost nil. What
then, is that moderate load by which we shall obtain the largest amount
of "useful effect"? this is a problem which many of the ablest engineers
and philosophers have endeavoured to solve; and the formulae--partly
based on theory and partly on experiment--which were used by Euler, are
generally accepted as a fair approximation. They are very simple, and
peculiarly interesting on account of their wide applicability. They are
equally true for me