have an intimate bearing on
the type of machine and media of transmission. This very circumstance
often compels giving away efficiency and convenience in some machines
to gain more in others. This is evident enough if the principal
origins of power generation be examined. They are in the main as
follows:--

_a_. Water-power available at the mine.
_b_. Water-power available at a less distance than three
or four miles.
_c_. Water-power available some miles away, thus necessitating
electrical transmission (or purchased electrical power).
_d_. Steam-power to be generated at the mine.
_e_. Gas-power to be generated at the mine.

_a_. With water-power at the mine, winding engines can be operated
by direct hydraulic application with a gain in economy over direct
steam, although with the sacrifice of control and reliability. Rods
for pumps can be driven directly with water, but this superiority
in working economy means, as discussed later, a loss of flexibility
and increased total outlay over other forms of transmission to pumps.
As compressed air must be transmitted for drills, the compressor
would be operated direct from water-wheels, but with less control
in regularity of pressure delivery.

_b_. With water-power a short distance from the mine, it would
normally be transmitted either by compressed air or by electricity.
Compressed-air transmission would better satisfy winding and drilling
requirements, but would show a great comparative loss in efficiency
over electricity when applied to pumping. Despite the latter drawback,
air transmission is a method growing in favor, especially in view
of the advance made in effecting compression by falling water.

_c_. In the situation of transmission too far for using compressed
air, there is no alternative but electricity. In these cases, direct
electric winding is done, but under such disadvantages that it
requires a comparatively very cheap power to take precedence over
a subsidiary steam plant for this purpose. Electric air-compressors
work under the material disadvantage of constant speed on a variable
load, but this installation is also a question of economics. The
pumping service is well performed by direct electrical pumps.

_d_. In this instance, winding and air-compression are well accomplished
by direct steam applications; but pumping is beset with wholly
undesirable alternatives, among which it is difficult to choose.

_e_. With internal combustion engine