H Y D 
The Char acters are, 
The flower has a permanent mpafcment of one leaf 
tut into five fiegments .which fipread open. It bath one 
bell-fhapcd petal which is divided into five parts y indented 
at their points j under each of thefie fiegments is fitted a 
nehiarium , which is fituated about the middle , and fihut 
up lengthways ■ by two lamelhe. It hath five Jfamina 
which are longer than the petals terminated by oblong 
profiler ate fummits , and an oval-pointed germen , J$p port- 
ing an awl-Jloaped ftyk the length of the jiamina , crowned 
by a bifid fpreading fiigma. The germen afterward be- 
comes a globular capfiule with one cell , inclofmg one large 
round feed. 
This genus of plants is ranged in the firft feftion 
of Linnaeus’s fifth clafs, intitled Pentandria Mono- 
gynia, which includes the plants whole flowers have 
five ftamina and one ftyl'e. 
We know but one Species of this genus, viz. 
Hydrqphyllon ( Virginianum ) foliis pinnatifidis. Lin. 
Sp. 208. Morini. Joncq.Hort. Water Leaf with wing- 
pointed leaves. 
This plant grows naturally in many parts of North 
America, on moift fpongy ground. The root 
of it is compofed of many ftrong flefby fibres, 
which fpread wide on every fide, from which arife 
many leaves with foot- (talks -five or fix inches long, 
which are jagged into three, five, or feven lobes, 
almoft to the midrib , thefe are indented on their 
edges, and have feveral veins running from the mid- 
rib to the Tides ; they are of a lucid green, and in the 
fpring have water Handing on the cavities, from 
whence I fuppofe Morinus gave it the title of Water 
Leaf, and not from the plant growing in water, as 
Tournefort conjectures. The flowers rife with foot- 
ftalks from the root, having one or two fmall leaves 
of the fame fhape with the lower ; the flowers are 
produced in loofe clufters hanging downward ; they 
are of a dirty white and bell-ihaped, fo make no 
great figure. They appear in June, and the feeds 
fometimes ripen here in Auguft. 
This plant is very hardy in refpect to cold, but it 
fhould be planted in a moift rich foil •, for if it is 
planted in a dry warm foil, it will not live, unlefs it 
is conftantly watered in dry weather. It may be pro- 
pagated by parting of the roots, which fhould be done 
in autumn, that the plants may be well rooted be- 
fore fpring, for otherwife they will require a great 
deal of water. It requires a moift foil and lhady 
fituation. 
HYDROPIPER, the common biting Arfe-fmart, 
which grows in great plenty in moift places near 
ditches Tides almoft every where. 
HYDROS T ATICS [uJ^oraLri, of water, 
and trdj iv.fi of raroj, '{landing, of Uv[m, I Hand or ftop ; 
Hydroftatics being conceived as the doftrine of the 
asqihiilibrum of liquors,] or the doftrine of the gra- 
vitation of fluid ; or it is that p2rt of the mechanics 
which confiders the weight or gra vity of fluid bodies •, 
particularly of wafer, and of folid bodies immerged 
therein. 
To Hydroftatics belongs whatever relates to the 
gravities and equilibria of liquors, with the art of 
weighing bodies in water, in order to eftimate their 
fpecific gravities. 
Of the ufe of this fcience in horticulture, the Rev. 
Dr. Hales, in his excellent Treatife of Vegetable Sta- 
ticks, has given many examples, by experiments, 
{hewing the quantities of moifture imbibed and per- 
fpired by plants and trees, neceftary to be known, in 
order to promote the bufinefs of vegetation. 
Some of the moft ufeful heads of this fcience are ; 
1 . That the upper parts of all fluids prefs upon the 
lower. 
2. That a lighter fluid may gravitate or prefs upon a 
heavier. 
3. That if a ; body that is contiguous to the water, 
be altogether, or in part, lower than the upper fur- 
face of the water, the lower part of the body will 
be prefled upwards by the water which touches it 
beneath. 
H Y t> 
4. There needs only a competent weight of an ex- 
ternal fluid, to account for the fifing of water ih 
pumps, See. 
5. It a body be placed under water, fo that its up- 
per mo ft furface lie parallel to the horizon, the direct 
p re fibre that it fuftains is no more than that of a co- 
lumn of water, whole bafe is the horizontal fuperficies 
of the body, and its heighth the perpendicular depth 
of the water. And if the water which leans on the 
body be contained in pipes which are open at both 
ends, the preffure of the water is to be eitimated 
by the weight of a pillar of water, the bafe of which 
is equal to the lower orifice of the pipe, and whole 
height is equal to a perpendicular, which reaches 
from thence to the top of the water, although the 
pipe fhould be much inclined any way, or though, 
it fhould be ever fo regularly ihaped, and much 
broader in fome other place than the bottom. 
6. A body which is immerfed in a fluid, fuftains a 
natural preffure from the fluid, which alfo increafes 
as the body is placed deeper beneath the furface of 
the fluid. 
7. The reafon why water afeends in fiphons, and 
by which it flows through them, may be explained 
from the external preffure of fome other fluid, with- 
out having recourfe to the abhorrence of a vacuum. 
8. The moft folid body, which will fink by its own 
weight at the furface, yet if it be placed at a depth 
twenty times greater than that of its own thicknefs 
it will not fink, if its defeent be not affifted by the 
incumbent water. 
9. If a body which is fpecifically lighter than a fluid, 
be immerfed in that fluid, it will rife with a force 
proportionable to the excefs of gravity in that fluid. 
10. If a body which is heavier than a fluid be im- 
merfed, it will fink with a force that is proportiona- 
ble to the excefs of its gravity. 
11. If any veffel be filled with water, or any other 
liquor, the furface of which is capable of being even, 
it will continue fo till difturbed by fome other exter- 
nal caufe. 
12. When the fluids are prefled, they are preffed 
undiquaque, i. e. on all Aides. 
How far the knowledge of any of thefe properties 
of fluids may conduce to the philofophical improve- 
ment of gardening, and the bufinefs of vegetation, 
will be more clearly perceived when well confidered 
by the ingenious artift, than being fet forth by words, 
rf Y G R O M E TER. [u of moift, and 
ft gov, meafure, of pfyw, to meafure,] is a machine 
or inftrument contrived to {hew or meafure, the 
moiftnefs and drinefs of the air, according as it 
abounds with moift or dry vapours, and to meafure 
and eftimate the quantity of fuch moiftnefs and 
drinefs. 
There are divers kinds of Hygrometers ; for what- 
ever body either fvvells or fhrinks by drinefs or moi- 
fture, is capable of being formed into an Hygrome- 
ter ; fuch are the woods of moft kinds, particularly 
Afh, Deal, Poplar, &c. fuch alfo is a cord, cat- 
gut, &c. 
Stretch a hempen cord or fiddle-ftring along a wall, 
bringing it over a truckle or pully *, and to the other 
end tie a weight, unto which fit a ftyle or index ; 
on the fame wall fit a plate of metal, divided into 
any number of equal parts, and the Hygrometer is 
complete. 
For it is a matter of undoubted obfervation, that 
moifture fenfibly fhortens the length of cords and 
firings ; and that as the moifture evaporates, they re- 
turn to their former length, and the like may be laid 
of a fiddle-ftring. 
The weight therefore, in the prelent cafe, upon an 
increafe of the moifture of the air, will afeend, and 
upon a diminution of the fame will defeend. 
Hence, as the index will Chew the fpaces of afeent and 
defeent, and thole fpaces are equal to the increments 
and decrements of the length of the cord or gut, the 
inftrument will difeover whether the air be more or 
lefs humid now, than it was at another given time. 
The 
