26 n a t u r a l h i s t o r y
©wing merely to the greatnefs ©f the heat, and the foickmefs of due
vapour in thofe wells, and not to a fulphureous or mineral halites:
That it is this thick vapour which extinguishes lights; and that the
tepid ftream is vifible in frofty weatherp: That it is from this tinder*
ground heat that the Water of our Rock-Springs is never frozen :
That we meet with the like warm watery vapour in Caves as wdl
as in Wells \ To fiipport this Hypothefis, he next produces ' his
diary of the Thermometer fufpended on different days for different
fpaces of time at different depths, and notes how much the Spirit in
the Thermometer did rife by the warmth o f his Wdl, above what
it was in the open air before he let it down. But) with great fob*
mifliorij nothing certain can be concluded from thefe experiments in
favour of the Hypothefis here efpoufed.
That it is warmer under-ground than it is above, efpedally in the
colder months o f the year, in which all Morton’s experiments were
made [; and that at a great depth there is a greater difference, other
circumftances being equal, betwixt the air underneath and that
above, than immediately or but a few feet under foe forface, muffc
be agreed ; but the queftion will remain to be decided, What this
difference is owing to ? The Atmofphere is ia congeries of many
bodies, air, folphur, nitre, fait, earth, and fire, and capable of
befog chilled or heated by the different drfperfion or combination o f
its own ufoal contents, as well as by the different influences of the
celeftial bodies. The air therefore is fubjedt to great alterations o f
heat and cold ; but where the air of the Atmofphere cannot reach,
a more even temperature prevails, and the cold o f the common air
fhall not afied the: air o f places with which it has not a free communication
any more than the heat: this is evident in puffing from the
open air into a dofe room; and in a mine Df well, where the aif
is lefs agitated hy tlie wind, and not fo mixed with the exhalations
\bhich occasioned cold and feoff as the air above, it is imp&flihk
hut it muff be warmer for foe generality, than k is upon foe forface
of the earth; and this is all that Morton s experiments prove. The
ingenious and accurate Dr. Hales having placed fix Thermometers,
one above ground, and foe reft ** with their balls inramerfed in the
earth, from two to 24 inches, at different depths, when the feoff
o f foe winter 1724 was fo intenfe as to freeze the forface of the
ftagnant Water near an inch thick, found that the Spirit in foe
Thermometer, which was exposed ifio foe open ait, was fallen four-
degrees below the freezing point; the Spirit of that whofe ball
was two inches under-ground, was four degrees alcove foe free«-
ing point; foe third, fourth, and fifth Thermometers, were pro-
9 Northamptonfhire, pag. 298« * page 360«
* Ibid. pag. 298. * From December 9, to March io.-
portionably
O F C O R N W A L L . z 7
jjortionably rais’d, as they were. deeper, to the fixth Thermometer,
which, being two feet underground, foe Spirit was ten degrees
... above the freezing point.” Veget. Stat. p. 348. Now what are
we to afcribe foefe different degrees of warmth unto? To fobter-
raneous fires, operating fo uniformly within two feet o f the forface?
No, certainly; but fo foe coldnefs of the air above, and to foe
more equal temperature o f the earth beneath, into which the cold of
foe air pierces lefs and lefs, in proportion to its diftance from the
forface, till at laft foe; variations of the air have no effedfc at all.
The truth is, fire is diftributed in every part of our globe; and in
foe bowels: .of the earth, it is not fobjeit to the checks and refiftance
©f cold, fo much as it is near foe forface; hence arifes a fenfible
difference; and it is warmer where this fire has liberty to aht, than
where it is controuled and repelled, by frefh and cold air. But this
foperiour heat below cannot be a canfe ©f fofilcient power to produce
foe effedt now in queftion; I .mean, foe Origin of Springs: this
univerfol fire, whilft itremains <h%eried in that harmlefs equilibrium
to which Providence has gracioufly deftined it, is weak and feeble,
and its power to evaporate Water, even under-ground, muft be
too final! and inconfiderable to give rife to all conflant Springs. I f
there were foch a fobterraneous central fire as fome learned men*
have fancy’d, conftantly exerting itfclfj and acting with a force gradually
greater as it is nearer to foe centre o f foe earth, this would
be a caufe fofficient, and equal to foe effe&; but that there is any
foch fete does by no means appear; neither is it conceivable that
any foch fire can fobfift without preying upon, and perpetually confirming,
the vitals of the earth. I f there was any foch fire, foe
deepest we defeend in mines foe hotter we fhould fed it, the heat
kicreafing by equal degrees foe nearer we approach foe foppofcd
region o f fire; but no foch regular increafe was found by foe fedu-
lous experiments o f Morton. In the fecond experiment Feb. 16,
at 9, a. m. foe Thermometer handing low, viz. at five decrees
below hard froft hi the open air, when fufpended for the fpace of
one hour in a Well, at the depth o f 25 feet, it rofe 14 degrees.
Feb. 27, 9 a. m. ftanding at two degrees below hard froft in the
air, when fufpended at foe depth of forty feet, it rofe ten degrees
in lefs than half an hour; and Feb. 24, 1703, (See foe ninth Experiment)
ftanding at half a degree below hard froft, it rofe fixteen
degrees in a quarter of an hour, when fufpended at forty fee t; and
when at hard froft, December *3, 1704, it rofe fixteen degrees in
a quarter of an hour, when fufpended at twenty-three feet two
ifeches (Experiment XII.): hence it appears, that when foe. fpirk
I Woodward Nat Hift. page j20. * B>* B- 300.
was