D E W 
in furface: that he filled them with pretty rrioift 
earth, taken off the furface of the ground, and they 
mcreafed in weight by the night’s dew 180 grains ; 
and decreafed in weight by the evaporation of the day 
j ounce 4- 282 grains. 
He fays likewife, he fet thefe in other broader pans 
to prevent any moifture from the earth flicking to the 
bottom of them. He adds, that the moifter the earth 
is, the more dew falls on it in a night, and more than 
a double quantity of dew falls on a furface of water 
than there does on an equal furface of moift earth. 
The evaporation of a furface of water in nine hours 
winter’s dry day, is A_ of an inch : the evaporation 
of a furface of ice fet in the fhade during a nine hours 
day, was T - r . 
So here are 540 grains more evaporated from the 
earth every 24 hours in fummer than fall in dew in 
the night; that is, in 21 days near 26 ounces from a 
circular area of a foot diameter; and circles being as 
the fquares of their diameters, 10 pounds 4- 2 ounces 
will in 2 1 days be evaporated from the hemifphere of 
30 inches diameter, which the Sunflower’s root occu- 
pies ; which, with the 29 pounds drawn off by the 
plant in the fame time, makes 39 pounds, that is, 9 
pounds and 4 out °f every cubic foot of earth, the 
plant’s roots occupying more than 4 cubic feet : but 
this is a much greater degree of arinefs than the fur- 
face of the earth ever fuffers for 1 5 inches depth, even 
in the drieft feafons in this country. 
In a long dry feafon therefore, efpecially within the 
tropics, we njuft have recourfe, for fufficient moifture 
to keep plants and trees alive, to the moift ftrata of 
earth, which lie next below that in which the roots 
are. 
Now moift bodies always communicate of their moif- 
ture to more dry adjoining bodies ; but this flow mo- 
tion of the afcent of moifture is much accelerated by 
the fun’s heat to confiderable depths in the earth, as 
is probable, he fays, from the twentieth experiment 
in the faid book. 
Now 180 grains of dew falling in one night on a cir- 
cle of a foot diameter = 113 fquare inches ; thefe 
180 grains being equally fpread on this furface, its 
depth will be T part of an inch = — • He adds, 
r 1 5 9 r 113 x 254 
that he found the dew in a winter night to be the ^ 
part of an inch ; fo that if we allow 1 5 1 nights for 
the extent of the fummer dew, it will in that time 
arife to one inch depth : and reckoning the remaining 
214 nights for the extent of the winter’s dew, it will 
produce 2,39 inches depth, which makes the dew of 
the whole year amount to 3,39 inches depth. 
And the quantity which evaporated in a fair fum- 
mer’s day from the fame furface, being as 1 ounce 
282 grains, gives fh? part of an inch depth for eva- 
poration, which is four times as much as fell at 
night. 
He fays likewife, that he found by the fame means, 
the evaporation of a winter’s day to be nearly the 
fame as in a fummer’s day ; for the earth being in 
winter more faturate with moifture, that excels of 
moifture anfwers to the exceflive heat in fummer. 
Nic. Cruquius, N° 381. of the Philofophical Tranf- 
aftions, found, that 28 inches depth evaporated in a 
whole year from water, i. e. -A- of an inch each day at 
a mean rate : but the earth in a fummer’s day evapo- 
rates -^g- of an inch, fo the evaporation of a furface 
of water is to the evaporation of a furface of earth in 
fummer as 10:3. 
The quantity of rain and dew that falls in a year is 
at a medium 22 inches. The quantity of the earth’s 
evaporation in a year is at leaft 9 4- L inches ; flnce 
that is the rate at which it evaporates in a fummer’s 
day : from which 9 + 4: inches are to be deducted 
3,39 inches for circulating daily dew, there remains 
6,2 inches ; which 6,2 inches deducted from the quan- 
tity of rain that falls in a year, there remains at leaft 
16 inches depth to repleniffi the earth with moif- 
ture for vegetation, and to fupply the fprings and 
rivers. 
D I A 
Dr. Hales proceeds to inftance, in the cafe’ of a Hop- 
ground which he gives in the ninth experiment of 'his 
book of Vegetable Statics, that the evaporation there 
found, from the Hops, conftdered only for three 
months, at x + r part of an inch, each day, which will 
be -At of an inch : but before it be allowed 6,2 inches 
to form the furface of the ground, which added to 
the -Aj- give 7,1 inches, which is the ucrnoft that can 
be evaporated from a furface of Hop-ground in a 
year; fo that of 22 inches depth of rain, there re- 
main 15 inches to fupply fprings, which are more or 
Ids exhaufted, according to the drinefs or wetnefs of 
the year. 
Hence we find, that 22 inches depth of rain in a, 
year is fufficient for all the purpofes of nature in fuch 
fiat countries as that about Teddington near Hamp- 
ton Court. But in the hill countries, as in Lanea- 
ffiire, there falls 42 inches depth of rain water, from 
which, ded lifting 7 inches for evaporation, there re- 
mains 35 inches depth of water for the fprings, be- 
hides great fupplies from much more plentiful dews 
than fall in plain countries ; which vaft (lores feem fo 
abundantly fufficient to anfwer the great quantity of 
water, which is conveyed away by the fprings and ri- 
vers from thofe hills, that we need not have recourfe 
for fupplies to the great abyfs, whofe furface at high 
water is furmounted fome hundreds of feet by thofe 
vaft hills from whence the longeft and greateft rivers 
take their rife. 
D I AN THERA. Lin. Gen. Plant. 37. Flor. Virg. 6 * 
The Characters are. 
The flower hath a permanent empalement of one leaf, which 
is tubulous , and cut at the top into five equal parts 5 the 
flower is of the grinning kind , having one petal with a 
fhort tube ; the upper lip is reflexed and bifid , the lower 
is divided into three parts , the middle being the broadefi ; 
it hath two fhort fender ftamina adhering to the 
back of the petal , one of thefe hath a twin fummit , the 
other is a little taller. It hath an oblong ger men, fupport- 
ing a fender flyle the length of the flamina , crowned by 
an obtufe fiigma. The empalement afterward becomes a 
capfule with two cells , opening with two valves , which 
are alternately compreffed at the top and bottom , and 
open with an elaficity , cafiing a Jingle fiat feed out of each 
cell. , 
This genus of plants is ranged in the firft feftion of 
Linnaeus’s fecond clafs, intitled Diandria Monogynia, 
the flower having two ftamina and one ftyle. This is 
one of the genera which, by Linnaeus’s method, is fe- 
parated to a great diftance from their congeners ; for 
by all their other charafters they ffiould be joined to 
his fourteenth clafs, but having only two ftamina, they 
are put under his fecond. 
We know but one Species of this genus at prefent, 
viz. 
Diamthera ( Americana ) fpicis folitariis alternis. Lin, 
Sp. 24. Di ant her a with folit ary alternate [pikes. 
This plant grows naturally in Virginia, and other 
parts of North America, from whence the feeds have 
been fent to England, where they have fucceeded. 
This is a low herbaceous plant with a perennial root, 
which fends out fever al weak ftalks about four inches 
long, garniffied with roundiffi leaves of an aromatic 
odour, (landing clofe to the ftalks ; they are hairy, 
and of a dark green colour ; from the fide of the 
ftalks the flowers are produced in fmall fpikes, placed 
alternately ; thefe are in fliape and colour very like 
thofe of the Clinopodium, but have only two ftamina 
in each. It flQwers the latter end of July, but rarely 
produces feeds in England. 
This plant is very difficult to preferve in this coun- 
try, for although it is hardy enough to live in the open- 
air in England, yet it is very lubjeft to rot in winter ; 
and if it is placed under fhelter, it is apt to draw up 
weak, and foon after decay, fo that at prefent the 
plants are rare in this country. 
DIANTHUS. Lin. Gen. Plant. 500. Cafyophyllus, 
Tourn. Xnft. R. EL 329. Clove Gilly Flower, Carna- 
tion Pink; in French, Oeillet. 
4 Y The 
