century ago, will not now drive a common mill". Befides, moft
woodlands, forefts, and chafes, with us abound with pools and
moraffes; no doubt for the reafon given above.
To a thinking mind few phenomena are more ftrange than the
ftate of little ponds on the fummits of chalk-hills, many of which
are never- dry in the moft trying droughts of fummer. On chalk-
bills I fay, becaufe in many rocky arid gravelly foils fprings ufually
break out pretty high on the fide’s of elevated grounds arid mountains
; but no perfon acquainted with chalky diftrifts will allow that
they ever faw fprings in fuch a foil but in vallies arid bottoms, linCe
the waters of fo pervious a ftratum as chalk all lie on one dead
level, as well-diggers have affured me again and again.
Now we have many fuch little round ponds in this diftridl; and
one in particular on our fheep-down, three hundred feet above my
houfe; which, though never above three feet deep in the middle,
and not more than thirty feet in diameter, and containing perhaps
riot more than two or three hundred hoglheads of water, yet never
is known to fail, though it affords drink for three hundred'or
four hundred Iheep, and for at leaft twenty head of large cattle
befide. This pond, it is true, is over-hung with two moderate
beeches, that, doubflefs, at times afford it much fitpply : but then
we have others as fmall, that, without the aid of trees, and in fpite
of evaporation from fun and wind, and perpetual corifumption by
cattle, yet conftantly maintain a moderate fhare of water, without
overflowing in the wetteft feafons, as they would do if fupplied by
fprings. By my journal of May, 1775, it appears that “ the fmall
“ and even confiderable ponds in the vales are now dried up, while
“ the fmall ponds on the very tops of hills are but little affedted.”
Can this difference be accounted for from evaporation alone, which
certainly is more prevalent in bottoms ? or rather have not thofe
Vide Kaim's Travels to North- America.
elevated
elevated pools fome unnoticed recruits, which in the night time
counterbalance the wafte of the day; without which the cattle alone
muft foon exhauft them ? And here it will be neceffary to enter
more minutely into the caufe. Tit .Hales, in hjsYegetable Statics, advances,
from experiment, that “ the moifter the earth is the more
“ dew falls on it in a night : and more than a double quantity of T f i
“ dew falls on a furface of water than there does on an equal
“ furface of moift earth.” Hence we fee that water, by it’s coolnefs,
is enabled to affimilate to itfelf a large quantity of moifture nightly
by condenfation; and that the air, when loaded with fogs and
vapours, and even with copious dews, can alone advance a confiderable
and neyerrfailing refource. Perfons that are much
abroad, and travel early and late; fuch as Ihepherds, fifhermen,
•&c. can tell what prodigious fogs prevail in the night on elevated
downs, even in the hotteft parts o f fummer; arid how much the
furfaces of things are drenched by thofefwimming vapours, though,
to the fenfes, all the while, little moifture feems tofall.
I am, &c.