back again to the highest point; it means the entire destruction of its
velocity, and it gives the maximum pressure obtainable from a jet of water
impinging upon a surface of any form whatsoever. The reaction noticed in
Fig. 3 as acting along _c_ B is now confronted by an impact of the now
horizontal stream as it is turned round the second 90 deg. of curvature,
and reacts also vertically downward. It would almost seem as if the first
reaction from B to F should be exactly neutralized by the second impact
from F to D. But such is not the case, as experiment shows an excess of the
second impact over the first reaction amounting to six units, and shows
also that the behavior of the stream through its second quadrant is
precisely similar in kind to the first, only less in degree. Also the
impact takes place vertically in one case and horizontally in the other.
The total downward pressure given by the stream when turned 180 deg. is
found by experiment thus: Total impact and reaction from 180 deg. change in
direction of current = 132 units; and by deducting the impact 71 units, as
previously measured, the new reaction corresponds with an increase of 61
units above the first impact. It also shows an increase of 37.75 units
above the greatest resultant obtained by the same stream turned through 90
deg. only. Therefore, in designing a screw propeller or turbine, it would
seem from these experiments desirable to aim at changing the direction of
the stream, so far as possible, into one at 180 deg. to its original
course, and it is by carrying out this view, so far as the necessities of
construction will permit, that the scientifically designed modern turbine
has attained to that prominence which it holds at present over all
hydraulic motors. Much more might be written to extend and amplify the
conclusions that can be drawn from the experiments described in the present
paper, and from many others made by the writer, but the exigencies of time
and your patience alike preclude further consideration of this interesting
and important subject.