than when it discharges freely in every direction. Experimentally this is
shown to be the case, for when the same oblong jet, discharged under the
same conditions, impinged vertically upon a smooth plate, and gave a
pressure of 71 units, gave 87 units when discharged into a confined
right-angled channel. This result emphasizes the necessity for confining
streams of water whenever it is desired to receive the greatest pressure by
arresting their velocity. Such streams will always endeavor to escape in
the directions of least resistance, and, therefore, in a turbine means
should be provided to prevent any lateral deviation of the streams while
passing through their buckets. So with screw propellers the great mass of
surrounding water may be regarded as acting like a channel with elastic
sides, which permits the area enlarging as the velocity of a current
passing diminishes. The experiments thus far described have been made with
jets of an oblong shape, and they give results differing in some degree
from those obtained with circular jets. Yet as the general conclusions from
both are found the same, it will avoid unnecessary prolixity by using the
data from experiments made with a circular jet of 0.05 square inch area,
discharging a stream at the rate of 40 ft. per second. This amounts to 52
lb. of water per minute with an available head of 25 ft., or 1,300
foot-pounds per minute. The tubes which received and directed the course of
this jet were generally of lead, having a perfectly smooth internal
surface, for it was found that with a rougher surface the flow of water is
retarded, and changes occur in the data obtained. Any stream having its
course changed presses against the body causing such change, this pressure
increasing in proportion to the angle through which the change is made, and
also according to the radius of a curve around which it flows. This fact
has long been known to hydraulic engineers, and formulæ exist by which such
pressures can be determined; nevertheless, it will be useful to study these
relations from a somewhat different point of view than has been hitherto
adopted, more particularly as they bear upon the construction of screw