f five compartments
with four full-sized haulage ways (Fig. 13), each of greater size
than in the above instance. In this case, the auxiliary engine
becomes a balanced one, and can be employed part of the time upon
ore-haulage. Such a shaft will be about 26 feet to 28 feet long
by 8 feet wide outside the timbers, when provision is made for
one gangway. The capacity of such shafts can be up to 4,000 tons a
day, depending on the depth and engine. When very large quantities
of water are to be dealt with and rod-driven pumps to be used,
two pumping compartments are sometimes necessary, but other forms
of pumps do not require more than one compartment,--an additional
reason for their use.

For depths greater than 3,000 feet, other factors come into play.
Ventilation questions become of more import. The mechanical problems
on engines and ropes become involved, and their sum-effect is to
demand much increased size and a greater number of compartments.
The shafts at Johannesburg intended as outlets for workings 5,000
feet deep are as much as 46 feet by 9 feet outside timbers.

It is not purposed to go into details as to sinking methods or
timbering. While important matters, they would unduly prolong this
discussion. Besides, a multitude of treatises exist on these subjects
and cover all the minutiae of such work.

SPEED OF SINKING.--Mines may be divided into two cases,--those
being developed only, and those being operated as well as developed.
In the former, the entrance into production is usually dependent
upon the speed at which the shaft is sunk. Until the mine is earning
profits, there is a loss of interest on the capital involved, which,
in ninety-nine instances out of a hundred, warrants any reasonable
extra expenditure to induce more rapid progress. In the case of
mines in operation, the volume of ore available to treatment or
valuation is generally dependent to a great degree upon the rapidity
of the extension of workings in depth. It will be demonstrated
later that, both from a financial and a technical standpoint, the
maximum development is the right one and that unremitting extension
in depth is not only justifiable but necessary.

Speed under special conditions or over short periods has a more
romantic than practical interest, outside of its value as a stimulant
to emulation. The thing that counts is the speed which can be maintained
over the year. Rapidity of sinking depends mainly on:--

_a_. Whether the sh