than usual, at the
West End: and when you get up to the clouds, and can walk into them
or out of them, as you like, you find when you're in them they wet
your whiskers, or take out your curls, and when you're out of them,
they don't; and therefore you may with probability assume--not with
certainty, observe, but with probability--that there's more water
in the air where it damps your curls than where it doesn't. If it
gets much denser than that, it will begin to rain; and then you
may assert, certainly with safety, that there is a shower in one
place, and not in another; and not allow the scientific people to
tell you that the rain is everywhere, but palpable in Tooley
Street, and impalpable in Grosvenor Square.

That, I say, is broadly and comfortably so on the whole,--and yet
with this kind of qualification and farther condition in the
matter. If you watch the steam coming strongly out of an
engine-funnel,[8]--at the top of the funnel it is transparent,--you
can't see it, though it is more densely and intensely there
than anywhere else. Six inches out of the funnel it becomes
snow-white,--you see it, and you see it, observe, exactly where it
is,--it is then a real and proper cloud. Twenty yards off the
funnel it scatters and melts away; a little of it sprinkles you
with rain if you are underneath it, but the rest disappears; yet it
is still there;--the surrounding air does not absorb it all into
space in a moment; there is a gradually diffusing current of
invisible moisture at the end of the visible stream--an invisible,
yet quite substantial, vapor; but not, according to our definition,
a cloud, for a cloud is vapor _visible_.

Then the next bit of the question, of course, is, What makes the
vapor visible, when it is so? Why is the compressed steam
transparent, the loose steam white, the dissolved steam transparent
again?

The scientific people tell you that the vapor becomes visible, and
chilled, as it expands. Many thanks to them; but can they show us
any reason why particles of water should be more opaque when they
are separated than when they are close together, or give us any
idea of the difference of the state of a particle of water, which
won't _sink_ in the air, from that of one that won't _rise_ in
it?[9]

And here I must parenthetically give you a little word of, I will
venture to say, extremely useful, advice about scientific people in
general. Their first business is, of course, to tell you things