[918.] The N.Z. Journal of Science and Technology. 273 
with the history of the steam-engine, for the first steam-engines were practi¬ 
cally all pumping-engines, and were employed in unwatering the Cornish 
tin-mines. Considering the low steam-pressure in use in the early days, 
and the crude appliances available for manufacturing these engines, the 
results obtained were remarkable. These results may be attributed to 
the Cornish cycle under which these engines worked, and to the very high 
vacuum which was obtained in this type of engine. Advantage was taken 
of the very heavy rods with which these engines operated the underground 
pumps, by utilizing the inertia of these rods to enable a good degree of 
expansion to be obtained, and their function may be compared to that of 
a fly-wheel on a rotative engine. 
The first application of electricity for the purpose of unwatering mines 
was not particularly successful, and there are numerous instances of 
electrically operated pumps being discarded and replaced by the older 
type of steam-engine. 
In metalliferous mines the shafts are usually of a smaller size than those 
in use in coal-mines, and a smaller amount of space is available for the 
necessary pump gear. Consequently the type of engine adopted generally 
operated only a single line of rods as compared with two lines of balanced 
rods in coal-mine engines. It will be readily understood that the problem 
of operating electrically a single line of heavy pump-rods calls for a good 
deal of mechanical ingenuity, and it was soon realized that this method of 
operating pumps was not the ideal one. Not only were mechanical diffi¬ 
culties experienced, but the efficiency of the whole plant was low when 
compared with the direct-coupled non-rotative steam-engine. 
So far we have only dealt with pumps underground operated by some 
form of power on the surface with mechanical connections between the 
prime mover and the pumps. In addition there were direct-driven steam, 
compressed-air, and hydraulic pumps. These pumps were erected in under¬ 
ground chambers at the various levels. The steam pumps were the means 
of introducing a considerable amount of heat into the mines—a very 
undesirable condition of affairs—whilst the steam-consumption was also 
heavy, and, notwithstanding the fact that advantage was taken of the 
inertia of the column of water to obtain expansion in the steam-cylinders, 
even then the thermo-dynamic efficiency was low. Mechanically they were 
fairly efficient and called for little in the way of heavy repairs. Their use 
has been practically discontinued. 
Compressed-air pumps, although notoriously inefficient, are still used to 
a great extent, but only where a comparatively small amount of power is 
necessary. They, however, have many practical advantages, and in shaft¬ 
sinking are useful in assisting ventilation. 
Hydraulic pumps, owing to the heavy pressures adopted, require careful 
handling. They possess the advantage that they may be worked when 
absolutely flooded, and this also applies to compressed-air pumps. 
It will thus be seen that the electrically operated pumps had to compete 
with the surface pumping-engine as regards efficiency and with the under¬ 
ground pumping-engines es regards convenience. There was also another 
very important point to be considered, and that was the question of 
the varying amount of water to be handled. With the pumps mentioned 
above, this problem was not a difficult one, and the efficiency at different 
loads did not vary to any great extent. Having realized that the correct 
method of applying the power to the pumps was to erect the whole of the 
plant underground, the manufacturers turned their attention to electrically 
18—Science. 
