that are so, and do happen,--as that, if you warm water, it will
boil; if you cool it, it will freeze; and if you put a candle to a
cask of gunpowder, it will blow you up. Their second, and far more
important business, is to tell you what you had best do under the
circumstances,--put the kettle on in time for tea; powder your ice
and salt, if you have a mind for ices; and obviate the chance of
explosion by not making the gunpowder. But if, beyond this safe and
beneficial business, they ever try to _explain_ anything to you,
you may be confident of one of two things,--either that they know
nothing (to speak of) about it, or that they have only seen one
side of it--and not only haven't seen, but usually have no mind to
see, the other. When, for instance, Professor Tyndall explains the
twisted beds of the Jungfrau to you by intimating that the
Matterhorn is growing flat;[10] or the clouds on the lee side of
the Matterhorn by the wind's rubbing against the windward side of
it,[11]--you may be pretty sure the scientific people don't know
much (to speak of) yet, either about rock-beds, or cloud-beds. And
even if the explanation, so to call it, be sound on one side,
windward or lee, you may, as I said, be nearly certain it won't do
on the other. Take the very top and center of scientific
interpretation by the greatest of its masters: Newton explained to
you--or at least was once supposed to have explained--why an apple
fell; but he never thought of explaining the exactly correlative,
but infinitely more difficult question, how the apple got up there!

You will not, therefore, so please you, expect me to explain
anything to you,--I have come solely and simply to put before you a
few facts, which you can't see by candlelight, or in railroad
tunnels, but which are making themselves now so very distinctly
felt as well as seen, that you may perhaps have to roof, if not
wall, half London afresh before we are many years older.

I go back to my point--the way in which clouds, as a matter of
fact, become visible. I have defined the floating or sky cloud, and
defined the falling, or earth cloud. But there's a sort of thing
between the two, which needs a third definition: namely, Mist. In
the 22d page of his 'Glaciers of the Alps,' Professor Tyndall says
that "the marvelous blueness of the sky in the earlier part of the
day indicated that the air was charged, almost to saturation, with
transparent aqueous vapor." Well, in certain wea