148 
POPULAR SCIENCE REVIEW. 
Engines of this description liave been long employed in the 
mining districts of this country and the Continent. Professor 
Eankin e states, that for the most successful application of 
these engines, as regards efficiency, it is necessary that the 
motion of the water should be slow, and as far as possible 
without shock. Three to six strokes per minute, or a velocity 
for the piston of one foot per second, is about the ordinary 
speed. The stroke also should be long, and therefore “ the 
most advantageous use to which a water-pressure engine can 
be put is the pumping of water, to which slow motion and a 
long stroke are well adapted, because they are favourable to 
efficiency, not only in the engine, but in the pump which it 
works.” 
Grinding, Crushing, and Cutting Machines . — The Exhibition 
has been fruitful in this department of machinery, some of 
them being exceedingly Avell constructed, and entitled to every 
commendation for the high finish bestowed upon them. Of 
late years corn-mills have been greatly improved, and the 
system of arranging the millstones in a line along one side of 
the mill, and rendering the whole of the processes self-acting 
by an improved system of cleaning, brushing, and separating 
the grain with elevators, Axchimeclian screw creepers, and an 
improved process of wire and silk dressing, give a degree of 
perfection to the manufacture that could not be attained when 
the grinding machinery was less perfect. Several small mills, 
chiefly on the French system of driving the stones with belts, are 
exhibited ; and others with high-pressure horizontal engines, 
driving from two to four pairs of stones, are entitled to notice 
for convenient arrangement and the superior finish of the 
workmanship. 
Several examples of machinery for the colonies are exhibited 
from Liverpool and Glasgow, and most of these are of a class 
calculated to meet all the requirements of complete trains of 
sugar-machinery ; as comprised in the steam-engine, rolls for 
crushing the sugar-canes, evaporating-pans, and centrifugal 
machines. In this description of machinery there is no par- 
ticular novelty or improvement, excepting only the steam- 
eugine, which of late has undergone some change in rendering 
the whole apparatus more portable and convenient for exporta- 
tation. In oil and powder mills the examples were not striking 
at the Exhibition, if we except the grinding and compressing 
apparatus of Messrs. Samuelson & Co., of Hull. That firm 
exhibited a complete set of hydraulic pumps and pipes, for 
extracting the oil from the seed inclosed in canvas bags. 
They also exhibited a pair of edge- stones in motion, which 
created considerable interest as a point of attraction to visitors 
during the exhibition. 
