the holes, appears quiet, or nearly quiet, when made to vibrate.
The separate drops will then be seen, and everything described in the
preceding pages, and a great deal more, will be evident. This is one of
the most fascinating experiments, and it is well worth while to make an
effort to succeed. The little motor that I used is one of Cuttriss and
Co.'s P. 1. motors, which are very convenient for experiments of this
kind. It was driven by four Grove's cells. These make it rotate too
fast, but the speed can be reduced by moving the brushes slightly
towards the position used for reversing the motor, until the speed is
almost exactly right. It is best to arrange that it goes only just too
fast, then the speed can be perfectly regulated by a very light pressure
of the finger on the end of the axle.

_Mr. Chichester Bell's Singing Water-jet._

For these experiments a very fine hole about one seventy-fifth of an
inch in diameter is most suitable. To obtain this, Mr. Bell holds the
end of a quill-glass tube in a blow-pipe flame, and constantly turns it
round and round until the end is almost entirely closed up. He then
suddenly and forcibly blows into the pipe. Out of several nozzles made
in this way, some are sure to do well. Lord Rayleigh makes nozzles
generally by cementing to the end of a glass (or metal) pipe a piece of
thin sheet metal in which a hole of the required size has been made. The
water pressure should be produced by a head of about fifteen feet. The
water must be quite free from dust and from air-bubbles. This may be
effected by making it pass through a piece of tube stuffed full of
flannel, or cotton-wool, or something of the kind to act as a filter.
There should be a yard or so of good black india-rubber tube, about
one-eighth of an inch in diameter inside, between the filter and the
nozzle. It is best not to take the water direct from the water-main, but
from a cistern about fifteen feet above the nozzle. If no cistern is
available, a pail of water taken up-stairs, with a pipe coming down, is
an excellent substitute, and this has the further advantage that the
head of water can be easily changed so as to arrive at the best result.

The rest of the apparatus is very simple. It is merely necessary to
stretch and tie over the end of a tube about half an inch in diameter a
piece of thin india-rubber sheet, cut from an air-ball that has not been
blown out. The tube, which may be of metal or of glass, may eith