Happy is the traveller who has the opportunity of hiring his cattle with
their attendants: for his delay and cares are then reduced to those of
making a bargain, and of riding what he has hired; and when one set of
animals is tired or worn out, he can leave them behind and ride on with
others. But, for 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 men, animals, or machines; and are wholly independent of
the way in which the power is applied: whether, for instance, a man
carries his burden, or draws it, or rows or punts it in a boat, or winds
it up with a crank or tread-mill.
Travellers might well turn the theory to account on their own behalf;
they are well situated for testing its truthfulness, by observing the
practices of the countries in which they are travelling. Reliable facts
upon the extreme distances that can be travelled over, day after day, by
people carrying different loads, but equally circumstanced in every other
respect, would be very acceptable to me.
The formulae are as follow:--Let b be the burden which would just
suffice to prevent an animal from moving a step; d the distance he could
travel daily if unloaded. Also, let b1 be some burden less than b; and
let d1 be the distance to which he could travel daily when carrying b1.