can claim no such distinction. Even
such problems as why the magnetic pole does not coincide with the
geographical, and why the force of terrestrial magnetism decreases from
the magnetic poles to the magnetic equator, as Humboldt first discovered
that it does, excite them only to lukewarm interest; for magnetism,
they say, is not known to have any connection whatever with climate or
weather.

EVAPORATION, CLOUD FORMATION, AND DEW

There is at least one form of meteor, however, of those that interested
our forebears whose meteorological importance they did not overestimate.
This is the vapor of water. How great was the interest in this familiar
meteor at the beginning of the century is attested by the number of
theories then extant regarding it; and these conflicting theories bear
witness also to the difficulty with which the familiar phenomenon of the
evaporation of water was explained.

Franklin had suggested that air dissolves water much as water dissolves
salt, and this theory was still popular, though Deluc had disproved it
by showing that water evaporates even more rapidly in a vacuum than
in air. Deluc's own theory, borrowed from earlier chemists, was that
evaporation is the chemical union of particles of water with particles
of the supposititious element heat. Erasmus Darwin combined the two
theories, suggesting that the air might hold a variable quantity of
vapor in mere solution, and in addition a permanent moiety in chemical
combination with caloric.

Undisturbed by these conflicting views, that strangely original
genius, John Dalton, afterwards to be known as perhaps the greatest
of theoretical chemists, took the question in hand, and solved it by
showing that water exists in the air as an utterly independent gas. He
reached a partial insight into the matter in 1793, when his first volume
of meteorological essays was published; but the full elucidation of
the problem came to him in 1801. The merit of his studies was at once
recognized, but the tenability of his hypothesis was long and ardently
disputed.

While the nature of evaporation was in dispute, as a matter of course
the question of precipitation must be equally undetermined. The most
famous theory of the period was that formulated by Dr. Hutton in a paper
read before the Royal Society of Edinburgh, and published in the volume
of transactions which contained also the same author's epoch-making
paper on geology. This "theory of rain" explained pr