lone must be provided. In net result,
no mineral deposit of speculative ultimate volume of ore warrants
an initial equipment of the sort that will meet every eventuality,
or of the kind that will give even the maximum efficiency which
a free choice of mining machinery could obtain.

_Third._--In the design and selection of mining machines, the safety
of human life, the preservation of the health of workmen under
conditions of limited space and ventilation, together with reliability
and convenience in installing and working large mechanical tools,
all dominate mechanical efficiency. For example, compressed-air
transmission of power best meets the requirements of drilling,
yet the mechanical losses in the generation, the transmission,
and the application of compressed air probably total, from first
to last, 70 to 85%.

_Fourth._--All machines, except those for shaft haulage, must be
operated by power transmitted from the surface, as obviously power
generation underground is impossible. The conversion of power into
a transmission medium and its transmission are, at the outset,
bound to be the occasions of loss. Not only are the various forms
of transmission by steam, electricity, compressed air, or rods, of
different efficiency, but no one system lends itself to universal
or economical application to all kinds of mining machines. Therefore
it is not uncommon to find three or four different media of power
transmission employed on the same mine. To illustrate: from the
point of view of safety, reliability, control, and in most cases
economy as well, we may say that direct steam is the best motive
force for winding-engines; that for mechanical efficiency and
reliability, rods constitute the best media of power transmission
to pumps; that, considering ventilation and convenience, compressed
air affords the best medium for drills. Yet there are other conditions
as to character of the work, volume of water or ore, and the origin
of power which must in special instances modify each and every one
of these generalizations. For example, although pumping water with
compressed air is mechanically the most inefficient of devices,
it often becomes the most advantageous, because compressed air may
be of necessity laid on for other purposes, and the extra power
required to operate a small pump may be thus most cheaply provided.

_Fifth._--Further limitations and modifications arise out of the
origin of power, for the sources of power