THE EXHIBITION OE 1862. 
145 
the whole of the river and mountain districts were searched for 
suitable sites for mills ; and for a series of years it was found 
necessary to take the mill to the power and not the power to 
the mill, as it has been since the introduction of steam. In 
some countries it is still desirable to employ water as a moving 
power, and hence follow the numerous improvements that have 
taken place in the construction of water-wheels, turbines, and 
other hydraulic machines. As late as 1830 water-power was 
still in demand in this country ; but from that time to the pre- 
sent it has been considered of little value unless it be in some 
districts where the power is considerable and where the weirs, 
aqueducts, and mill dams already exist. For a number of 
years the mills for cotton, corn, and flax were turned by water, 
and the construction of water-wheels was greatly improved by 
making them entirely of iron, which took place at the begin- 
ning of the present century. The late Mr. T. C. Hewes was 
one of the earliest improvers of water-wheels on the suspension 
principle, and this was followed by a new system of ventilation, 
by which the buckets were relieved of air on the entrance of 
the water, and subsequently restored at the lowest point of 
discharge. By this ingenious but simple contrivance the duty 
of the water-wheel was raised to a maximum, and the con- 
struction of water-wheels composed of iron arrived at a very 
perfect state. It was at this time that the investigations of 
Poncelet and the perseverance of Fourneyron introduced the 
horizontal wheel, founded on principles established by the 
former and adopted, after careful experiments, in the shape of 
the turbine by the latter. For several years the turbine made 
slow progress, as its advantages were not superior to that of 
the water-wheel, which maintained and still retains its reputa- 
tion in regard to the amount of work done with a given quantity 
of water. The turbine, however, occupied less space, was 
somewhat cheaper in its original cost, and became general on 
the Continent and America. Of late years the turbine has 
been greatly improved in this country, and we have several 
admirable specimens in the Exhibition, a few of which it will 
be proper to notice. 
In every description of machine recipient of water it is a 
universal condition that the water, to attain its full efficiency, 
should make its entrance and take its departure at a slow 
velocity. This has never been done with the turbine, but a 
close approximation has been attained by the best-constructed 
water-wheel. Smeaton, in his experiments on water-wheels, 
attained something above 80 per cent, of the theoretical fall, 
and some of the best wheels of the present time have arrived 
close upon that point of efficiency. Now, the best-constructed 
turbines seldom exceed from 65 to 70 per cent. There are, 
