ally, which is very annoying in
a difficult experiment. I have made for myself the pipe of which Fig. 67
is a full size representation, and I do not think that it is possible to
improve upon this. Those who are not glass-blowers will be able, with
the help of cork, to make a pipe with a trap as shown in Fig. 68, which
is as good, except in appearance and handiness.

In knocking bubbles together to show that they do not touch, care must
be taken to avoid letting either bubble meet any projection in the
other, such as the wire ring, or a heavy drop of liquid. Either will
instantly destroy the two bubbles. There is also a limit to the violence
which may be used, which experience will soon indicate.

In pushing a bubble through a ring smaller than itself, by means of a
flat film on another ring, it is important that the bubble should not be
too large; but a larger bubble can be pushed through than would be
expected. It is not so easy to push it up as down because of the heavy
drop of liquid, which it is difficult to completely drain away.

[Illustration: Fig. 67. Length of Stem 9 Inches]

[Illustration: Fig. 68. Length of Stem 9 Inches]

To blow one bubble inside another, the first, as large as an average
orange, should be blown on the lower side of a horizontal ring. A light
wire ring should then be hung on to this bubble to slightly pull it out
of shape. For this purpose thin aluminium rings are hardly heavy enough,
and so either a heavier metal should be used, or a small weight should
be fastened to the handle of the ring. The ring should be so heavy that
the sides of the bubble make an angle of thirty or forty degrees with
the vertical, where they meet the ring as indicated in Fig. 56. The
wetted end of the pipe is now to be inserted through the top of the
bubble, until it has penetrated a clear half inch or so. A new bubble
can now be blown any size almost that may be desired. To remove the pipe
a slow motion will be fatal, because it will raise the inner bubble
until it and the outer one both meet the pipe at the same place. This
will bring them into true contact. On the other hand, a violent jerk
will almost certainly produce too great a disturbance. A rather rapid
motion, or a slight jerk, is all that is required. It is advisable
before passing the pipe up through the lower ring, so as to touch the
inner bubble, and so drain away the heavy drop, to steady this with the
other hand. The superfluous liquid can then