66 
On Water Supplies suited to 
consumption of 250 cubic feet of gas. Assuming it to be worth 
2s. per thousand cubic feet, the cost would be 6c?., or only \d. 
per thousand gallons. The great advantages of gas-engines 
are, that they occupy little space, they can be started at a 
minute's notice, they require very little water to cool the work- 
ing parts, and neither time nor fuel is lost in getting them ready 
for work. 
In many instances it would be convenient to have the motor and 
pump combined in one machine, and the makers of the motors 
would readily furnish such combinations ; but it is very commonly 
more advantageous to arrange the pumps separately and drive 
them either by means of a belt or by gearing from the crank- 
shaft of the motors. One reason for preferring the separate 
arrangement is, that small motors generally run two or three 
times as fast as it is desirable to work pumps, hence some means 
of reducing speed is necessary. 
Wells. 
The last sources of supply to which I will allude are wells. 
They are the most common, and at the same time, for small 
supplies, the most objectionable and dangerous. 
The reason for this perhaps startling opinion is, that the 
water in wells is practically stagnant, and the air over the water 
is frequently so deficient in oxygen that it will not support com- 
bustion, hence there is little or no self-purifying power in the 
water, and if it become contaminated it cannot free itself from 
the evil, and while water has small power of self-purification 
it is peculiarly liable to pollution. Wells are generally lined 
with very open brickwork, by no means water-tight ; they stand 
in the midst of buildings, sunk in ground, the upper strata of 
which are often deeply impregnated by organic contamination 
proceeding from the usual surroundings of a dwelling-house or 
homestead, and such contamination is washed down in wet 
weather, some of it finding its way into the well. §ewers 
frequently pass close to wells, they are rarely water-tight, and 
leakage from them also gravitates to the lowest point, that is, 
the well, and cases have even occurred where negligent or 
indolent workmen and unscrupulous contractors have actually 
allowed drains to discharge into wells, and the disgusting 
offence has not been discovered till the outbreak of an epidemic 
has directed attention to the water-supply. In the case of 
draw-wells, much water is slopped about all round the well, 
becomes contaminated, and finds its way back again. Dogs, 
cats, rats, mice, domestic fowls, birds, and all manner of insects 
and creeping things fall in, decay, and become gradually dis- 
