s (Fig. 43). The effect of
different notes could be very easily shown if any one were to sing to
the piece of wood by which the jet is held. I can make noises of
different pitches, which for this purpose are perhaps better than
musical notes, and you can see that with every new noise the fountain
puts on a different appearance. You may well wonder how these trifling
influences--sealing-wax, the smoky flame, or the more or less musical
noise--should produce this mysterious result, but the explanation is not
so difficult as you might expect.

I hope to make this clear when we meet again.

LECTURE III.

At the conclusion of the last lecture I showed you some curious
experiments with a fountain of water, which I have now to explain.
Consider what I have said about a liquid cylinder. If it is a little
more than three times as long as it is wide, it cannot retain its form;
if it is made very much more than three times as long, it will break up
into a series of beads. Now, if in any way a series of necks could be
developed upon a cylinder which were less than three diameters apart,
some of them would tend to heal up, because a piece of a cylinder less
than three diameters long is stable. If they were about three diameters
apart, the form being then unstable, the necks would get more pronounced
in time, and would at last break through, so that beads would be formed.
If necks were made at distances more than three diameters apart, then
the cylinder would go on breaking up by the narrowing of these necks,
and it would most easily break up into drops when the necks were just
four and a half diameters apart. In other words, if a fountain were to
issue from a nozzle held perfectly still, the water would most easily
break into beads at the distance of four and a half diameters apart, but
it would break up into a greater number closer together, or a smaller
number further apart, if by slight disturbances of the jet very slight
waists were impressed upon the issuing cylinder of water. When you make
a fountain play from a jet which you hold as still as possible, there
are still accidental tremors of all kinds, which impress upon the
issuing cylinder slightly narrow and wide places at irregular distances,
and so the cylinder breaks up irregularly into drops of different sizes
and at different distances apart. Now these drops, as they are in the
act of separating from one another, and are drawing out the waist, as
you have seen