275 
1918.] The N.Z. Journal of Science and Technology. 
cheap electric power, the turbine pump is probably the most suitable, 
whilst where the cost of power is high the three-throw pump has the 
advantage, and that when dealing with a small amount of water the 
latter pump also is most advantageous. 
Direct current is most suitable where there is a big variation in the 
amount of water to be pumped, owing to the ease in which the speed of the 
motor can be varied, but alternating current possesses simplicity and the 
possibility of using much higher voltages than are practicable with direct 
current. 
In laying out any electrical pumping scheme it is of vital importance 
that the plant be arranged so that in the event of a sudden rush of water 
being met with, should the failure of the power or pumps occur, the pumps 
can be immediately raised. In other words, stationary electric pumps 
should not be installed where there is a possibility of their being flooded. 
The water in the lower section of the mine should be handled by means 
of suspended electric pumps connected to a capstan situated either on the 
surface or in a chamber underground, free from the danger of flooding. 
Winding .—Probably the most strenuous work which the electric motor 
is called upon to do in gold-mining is in connection with winding. In order 
to appreciate the difficulties to be met in this department it must be 
realized that the engine has to start with the full load, to accelerate rapidly 
up to full speed, and then, towards the end of the wind, to retard. In order 
that the minimum amount of time be taken during each wind, the periods 
of acceleration and retardation must be as short as possible, and this 
necessitates a large amount of reserve power and adequate braking-capacity. 
The conditions of winding in a gold-mine are much more strenuous 
than those encountered in a coal-mine. In the latter case there is usually 
only one level, but in the former the engine may be called upon to handle 
ore from a large, number of levels, consequently it is necessary that either 
one or both of the winding-drums be equipped with a clutch. It follows 
also that the engine must, at times, be capable of raising the whole load 
in an unbalanced state—that is, receiving no benefit from the rope, cage, 
and empty truck in the other compartment. In addition to the above, it 
is necessary for the purpose of shaft-inspection that the engine be capable 
of winding at a very low speed, and of easy manipulation at the various 
levels and at the collar of the shaft. Efficient overwinding-devices are also 
essential. 
The steam winding-engine has reached a great state of perfection, and 
is capable of adequately dealing with all the foregoing conditions, but it 
cannot be classed as a very economical prime mover. However, when the 
electric winder appeared in the field, steps were taken to improve the steam- 
consumption, and this was done by compounding the engine—usually two 
sets of compound tandem engines being used—adding an air-pump and 
condenser to the engine, and, in the case of existing engines, by utilizing 
the exhaust steam in conjunction with suitable steam-accumulators for 
driving exhaust-steam turbines for generating electricity for general use 
around the mine. 
All these things tended to complicate the winding plant, and as a 
winding-machine must be essentially reliable, apart from any consider¬ 
ations of economy, many users, especially colliery-owners, preferred to 
sacrifice economy for reliability. Electrical engineers had a very difficult 
problem to solve when they began to electrify winding-engines, but the 
proof that they have satisfactorily dealt with the matter lies in the fact 
