[Illustration: Diagram of apparatus as described in text]
Let there be a vessel, A B, (fig. 3.) containing water, on which a
small basin, C D, floats, having its mouth covered with the lid C D.
Through this lid and the bottom of the basin insert one leg of the
siphon soldering it into the holes with tin. Let the other leg be
outside the vessel A B, having its mouth lower than the surface of
the water in A B. If we draw the air in the siphon through the outer
extremity, the water will at once follow because of the impossibility
of a continuous vacuum in the siphon; and the siphon, having begun to
flow, flows on until it has exhausted all the water in the vessel:
but the discharge will be uniform, since the projection of the outer
leg below the surface of the water does not vary; for, as the vessel
becomes empty, the basin sinks with the siphon. The greater the excess
of the outer leg the greater will be the velocity of the discharge, yet
still uniform. In the figure, E F G is the siphon described, and the
surface of the water is in the line H K.
4. _Siphon which is capable of discharging a greater or less quantity
of Liquid with uniformity._
[Illustration: Diagram of apparatus as described in text]
By the following arrangement we can produce a discharge at once uniform
and variable; that is, a discharge in which, for a certain time at
pleasure, the stream continues uniform from the beginning, and again,
for any other period, is slower or quicker than before, but still
uniform with itself. As before, let A B (fig. 4.) be a vessel of water,
and C D a basin. Into the lid and bottom of the basin solder a tube L
M wider than the inner leg of the siphon. On the lid place a wooden
frame, C N X D, consisting of two upright pieces and a third lying
across them on the top. In the inner sides of the upright pieces let
grooves be cut down their whole length, along which another piece O P
is to move freely. Let R S be a screw, working perpendicularly in the
direction of the lid C D, and passing through a hole in O P: in O P let
a pin be so fixed as to enter the spiral thread of the screw. The screw
must project above N X, and a handle be fastened to its top by which
to turn it, and by this means O P can be raised or lowered. Let the
inner leg of the siphon be fixed in O P, and pass through the tube L
M, so that its mouth may dip into the water in the vessel. Now if, as
before, we draw off the liquid through the outer mouth, the siphon will
flow with a uniform stream until the whole be exhausted. And when it
is wished that a quicker stream should be produced through the siphon,
but uniform with itself, let the screw be turned so as to lower the
board O P; for then the excess of the outer leg is increased, and thus
the stream is still of uniform velocity, but quicker than before. If a
still greater velocity is desired, turn the screw again, so as to lower
O P still further; and if a less velocity is sought, let O P be raised.
Thus a discharge is produced through a siphon in one sense uniform, in
another variable.