loosely packed than the others the
difference is perceived on handling them. Or it may have one end
heavier than the other, or else its weight may not be equally
distributed round its axis, causing it to rest on the table with the
same part always lowermost; differences due to these causes are also
easily perceived when handling the cartridges. Again, one of two
similar cartridges may balance perfectly in all directions, but the
weight of one of them may be disposed too much towards the ends, as
in a dumb-bell, or gathered too much towards the centre. The period
of oscillation will differ widely in the two cases, as may be shown
by suspending the cartridges by strings round their middle so that
they shall hang horizontally, and then by a slight tap making them
spin to and fro round the string as an axis.

The touch is very keen in distinguishing all these peculiarities. I
have mentioned them, and might have added more, to show that
experiments on sensitivity have to be made in the midst of pitfalls
warily to be avoided. Our apparently simplest perceptions are very
complex. We hardly ever act on the information given by only one
element of one sense, and our sensitivity in any desired direction
cannot be rightly determined except by carefully-devised apparatus
judiciously used.

WHISTLES FOR AUDIBILITY OF SHRILL NOTES.

I contrived a small whistle for conveniently ascertaining the upper
limits of audible sound in different persons, which Dr. Wollaston
had shown to vary considerably. He used small pipes, and found much
difficulty in making them. I made a very small whistle from a brass
tube whose internal diameter was less than one-tenth of an inch in
diameter. A plug was fitted into the lower end of the tube, which
could be pulled out or pushed in as much as desired, thereby causing
the length of the bore of the whistle to be varied at will. When the
bore is long the note is low; when short, it is high. The plug was
graduated, so that the precise note produced by the whistle could be
determined by reading off the graduations and referring to a table.
(See Appendix.)

On testing different persons, I found there was a remarkable falling
off in the power of hearing high notes as age advanced. The persons
themselves were quite unconscious of their deficiency so long as
their sense of hearing low notes remained unimpaired. It is an only
too amusing experiment to test a party of persons of various ages,
including s