has been advanced to a point that warrants a large or
final installation. Moreover, even were the full possibilities of
the mine known, the limitations of finance usually necessitate a
less plant to start with than is finally contemplated. Therefore
output and equipment are usually growing possibilities during the
early life of a mine.

There is no better instance in mine engineering where pure theory
must give way to practical necessities of finance than in the
determination of the size of equipment and therefore output. Moreover,
where finance even is no obstruction, there are other limitations
of a very practical order which must dominate the question of the
size of plant giving the greatest technical economy. It is, however,
useful to state the theoretical considerations in determining the
ultimate volume of output and therefore the size of equipments,
for the theory will serve to illuminate the practical limitations.
The discussion will also again demonstrate that all engineering
is a series of compromises with natural and economic forces.

OUTPUT GIVING LEAST PRODUCTION COST.--As one of the most important
objectives is to work the ore at the least cost per ton, it is
not difficult to demonstrate that the minimum working costs can
be obtained only by the most intensive production. To prove this,
it need only be remembered that the working expenses of a mine
are of two sorts: one is a factor of the tonnage handled, such as
stoping and ore-dressing; the other is wholly or partially dependent
upon time. A large number of items are of this last order. Pumping
and head-office expenses are almost entirely charges independent
of the tonnage handled. Superintendence and staff salaries and
the like are in a large proportion dependent upon time. Many other
elements of expense, such as the number of engine-drivers, etc., do
not increase proportionately to increase in tonnage. These charges,
or the part of them dependent upon time apart from tonnage, may be
termed the "fixed charges."

There is another fixed charge more obscure yet no less certain.
Ore standing in a mine is like money in a bank drawing no interest,
and this item of interest may be considered a "fixed charge," for
if the ore were realized earlier, this loss could be partially
saved. This subject is further referred to under "Amortization."

If, therefore, the time required to exhaust the mine be prolonged
by the failure to maintain the maximum output, the