s to test the
truth of the explanation, I shall reverse the usual order, and show one
or two experiments first, which I think you will all agree are so like
magic, so wonderful are they and yet so simple, that if they had been
performed a few hundred years ago, the rash person who showed them might
have run a serious risk of being burnt alive.

[Illustration: Fig. 41.]

[Illustration: Fig. 42.]

You now see the water of the jet scattering in all directions, and you
hear it making a pattering sound on the paper on which it falls. I take
out of my pocket a stick of sealing-wax and instantly all is changed,
even though I am some way off and can touch nothing. The water ceases
to scatter; it travels in one continuous line (Fig. 42), and falls upon
the paper making a loud rattling noise which must remind you of the rain
of a thunder-storm. I come a little nearer to the fountain and the water
scatters again, but this time in quite a different way. The falling
drops are much larger than they were before. Directly I hide the
sealing-wax the jet of water recovers its old appearance, and as soon
as the sealing-wax is taken out it travels in a single line again.

Now instead of the sealing-wax I shall take a smoky flame easily made by
dipping some cotton-wool on the end of a stick into benzine, and
lighting it. As long as the flame is held away from the fountain it
produces no effect, but the instant that I bring it near so that the
water passes through the flame, the fountain ceases to scatter; it all
runs in one line and falls in a dirty black stream upon the paper. Ever
so little oil fed into the jet from a tube as fine as a hair does
exactly the same thing.

[Illustration: Fig. 43.]

I shall now set a tuning-fork sounding at the other side of the table.
The fountain has not altered in appearance. I now touch the stand of the
tuning-fork with a long stick which rests against the nozzle. Again the
water gathers itself together even more perfectly than before, and the
paper upon which it falls is humming out a note which is the same as
that produced by the tuning-fork. If I alter the rate at which the water
flows you will see that the appearance is changed again, but it is never
like a jet which is not acted upon by a musical sound. Sometimes the
fountain breaks up into two or three and sometimes many more distinct
lines, as though it came out of as many tubes of different sizes and
pointing in slightly different direction