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
|       |         |          |  ABS.
-----------------------------+-------+---------+----------+-

------
Smooth London tube, 13/4 in.   |  71   |   62    |  94.25   |   49 deg.
mean radius.               |       |         |          |
|       |         |          |
Rough wrought iron tube,     |  78   |   52    |  98.75   |  56.5 deg.
13/4 in.                     |       |         |          |
|       |         |          |
Smooth leaden tube bent to a |  71   |   40    |  81.5    |   60
sharp right angle.         |       |         |          |
-----------------------------+-------+---------+----------+-

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The third column is obtained by constructing a parallelogram of forces, where impact and reaction form the measures of opposing sides, and it furnishes the resultant due to both forces.  The fourth column gives the inclination ABS, at which the line of impact must incline toward a plane surface RS, Fig. 3, so as to produce this maximum resultant perpendicularly upon it; as the resultant given in column 3 indicates the full practical effect of impact and reaction.  When a stream has its direction changed to one at right angles to its original course, and as such a changed direction is all that can be hoped for by ordinary