ecause the brush
is wet. Now let us try the experiment; but as you cannot see this brush
across the room, I hold it in front of the lantern, and you can see it
enlarged upon the screen (Fig. 1, left hand). Now it is dry, and the
hairs are separately visible. I am now dipping it in the water, as you
can see, and on taking it out, the hairs, as we expected, cling
together (Fig. 1, right hand), because they are wet, as we are in the
habit of saying. I shall now hold the brush in the water, but there it
is evident that the hairs do not cling at all (Fig. 1, middle), and yet
they surely are wet now, being actually in the water. It would appear
then that the reason which we always give is not exactly correct. This
experiment, which requires nothing more than a brush and a glass of
water, then shows that the hairs of a brush cling together not only
because they are wet, but for some other reason as well which we do not
yet know. It also shows that a very common belief as to opening our eyes
under water is not founded on fact. It is very commonly said that if you
dive into the water with your eyes shut you cannot see properly when you
open them under water, because the water gums the eyelashes down over
the eyes; and therefore you must dive in with your eyes open if you wish
to see under water. Now as a matter of fact this is not the case at all;
it makes no difference whether your eyes are open or not when you dive
in, you can open them and see just as well either way. In the case of
the brush we have seen that water does not cause the hairs to cling
together or to anything else when under the water, it is only when taken
out that this is the case. This experiment, though it has not explained
why the hairs cling together, has at any rate told us that the reason
always given is not sufficient.

I shall now try another experiment as simple as the last. I have a pipe
from which water is very slowly issuing, but it does not fall away
continuously; a drop forms which slowly grows until it has attained a
certain definite size, and then it suddenly falls away. I want you to
notice that every time this happens the drop is always exactly the same
size and shape. Now this cannot be mere chance; there must be some
reason for the definite size, and shape. Why does the water remain at
all? It is heavy and is ready to fall, but it does not fall; it remains
clinging until it is a certain size, and then it suddenly breaks away,
as if whatever