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 formulae 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
propellers and turbines; and by directing the stream, AB, Fig. 3,
vertically into a tube 3/8 in. internal diameter and bent so as to turn the
jet horizontally, and placing the whole arrangement upon a compound
weighing machine, it is easy to ascertain the downward pressure, AB, due to
impact, and the horizontal pressures, CB, due to reaction. In theoretical
investigations it may be convenient to assume both these pressures exactly
equal, and this has been done in the paper "On Screw Propellers" already
referred to; but this brings in an error of no importance so far as general
principles are involved, but one which destroys much of the value such
researches might, otherwise possess for those who are engaged in the
practical construction of screw propellers or turbines. The downward impact
pressure, AB, is always somewhat greater than the horizontal reaction, BC,
and any proportions between these two can only be accurately ascertained by
trials. In these particular experiments the jet of water flowed 40 ft. per
second through an orifice of 0.05 square inch area, and in every case its
course was bent to a right angle. The pressures for impact and reaction
were weighed coincidently, with results given by columns 1 and 2, Table II.

[Illustration: FIG. 3]

[Illustration: FIG. 4]

_Table II.--Impact and Reaction in Confined Channels._

-----------------------------+-------+---------+----------+-------
Number of column. | 1 | 2 | 3 | 4
-----------------------------+-------+---------+----------+-------
Description of experiments. |Impact.|Reaction.|Resultant.| Angles
| |