LEV 
A water Level Ihews the horizontal line, by means 
of a furface of water, or other liquid, founded on 
this principle. That water always naturally places it- 
felf level. 
The moft Ample inftrument for this ufe is made 
of a long wooden trough, or canal, whofe fides are 
parallel to its bafe, fo that, being equally filled with 
water, the furface thereof £hews the line of Level. 
This Level is alfo made with two cups fixed to the 
two ends of a pipe three or four feet long, about an 
inchin diameter ; by means whereof, the water coni' 
municates from the one to the other cup, and this 
pipe being moveable on its Hand, by means of a 
ball and focket, when the two cups become equally 
full of water, the two furfaces mark the line of Level. 
Inftead of cups, this inftrument may be made with 
two ftiort cylinders of glafs three or four inches long, 
fattened to each end of the pipe with wax or maftich •, 
then the pipe, being filled either with common or co- 
loured water, will fhew itfelf through the cylinder, by 
means of which the line of Level is determined, the 
height of the water, with refpedt to. the center of 
the earth, being always the fame in both cylinders. 
This Level is very commodious in levelling fmall 
diftances. 
If you would level any piece of ground that you can 
fee from fide to fide, or from the middle to any fide, 
fet up your inftrument in the middle of it, whether it 
be a water Level, or a ground Level with fights ; 
place it fo high, that you may fee over the higheft part 
of the ground half a foot or a foot ; then let up a 
flake in the middle, fo that the top may be exabtly 
level with the fights, and another ftake on the higheft 
fide, the top of which mull be level with the middle 
flake; then either turn the Level, or look-back fight, 
and fet up another ftake on the lower ground level 
with the two firft ; then you will have three Hakes 
(landing in a Level. 
Then keeping your Level true to the middle ftake, 
turn it till it makes right angles with the three Hakes, 
and fet up two flakes on each fide one Level with 
thofe three, then you will have five ftakes in two lines 
fet true level. 
If the ground be large, you may fet up two rows 
more by the Level, but five ftakes are enough in a 
(mail ground. 
When this is done, you may lay your Level afide, 
and look over the head of one to the head of another, 
and caufe the perfon who affifts you to put down 
flakes between two and two, till you have fet as many 
flakes lever in the ground as you think convenient ; or 
you may ufe a rule, which being placed level with 
the head of the ftake, you may look over that to the 
head of the other, and put ftakes down between you 
and the other ftake, to what number you pleafe. 
The ground being thus flaked out with all the ftakes 
heads level, and half a foot higher than the higheft 
ground, in fome grounds the middle ftake, and the 
ftakes in the crofs line, will be the Level line the 
ground muft be brought to ; that is, abating the hill, 
and filling up the low fide to the Level of the mid- 
line. But if the ground be very uneven, then you 
muft meafure over all the ftakes, and take them mid- 
dle high for their mean of Level, and, by the rule 
of three, proportion your ground to that. 
As for inftance : If a valley be ten poles in length, 
and two feet in depth from the ftrait line, and there 
be a hill five poles long ; how many feet deep muft a 
perfon fink thofe five poles to fill up the valley ? 
This queftion may be refolved by the inverfe or back 
rule of three, and will Hand thus : As 5 to 2, fo is 
io to 4. 
$ — — 2 - — -- 10 
2 
5)20(4 
So that a perion muft go four feet deep in fuch a hill 
to make good fuch a valley. 
If you are to abut the top of the hill four feet deep, 
L I C 
and two poles from the top of that hill, thole four 
feet are to come out. 
To perform this, fet up a ftake on the top of a hill 
two or three feet above ground, and another of the 
fame height where the depth comes out, fet down a 
ftake three rods from that, till the head comes t04.be 
in a line with thefe two, and at that ftake you muft be 
one foot deep. - 
At fix poles ftake down another as before, and there 
you muft be two feet deep : then ftake down another 
at nine poles, and there you muft be three feet 
deep, and you may fet more ftakes at equal dif- 
tances, which will direct you fo as that you cannot 
go amifs. 
LEVITY is the privation or want of weight in 1 any 
body, when compared with another which is heavier, 
in which fenfe it is oppofed to gravity. 
The fchoolmen maintain, that there is fuch a thing as 
pofitive and ablblute Levity, and impute this to the 
fife and emergency of bodies lighter in fpecie than 
the fluids wherein they rife. 
But, befides that the common fenfe of mankind dif- 
covers, that Levity is only a relative term, we find 
that all bodies tend towards the earth, fome flower, 
and fome fafter, in all fluids or mediums, whether 
water, air, &c. 
Thus cork is faid to be lighter than gold, becaufe 
under equal dimenfions of bulk the gold will fink in, 
and the cork fwirn upon the water. 
Archimedes has demonftrated. That a folid body 
will float any where in a fluid of the fame lpecific 
gravity, and that a lighter body will keep above a 
heavier. 
The reafori of this is, becaufe bodies falling towards 
the earth, thofe which have a like number of equal 
parts, have equal gravity, fince the gravity of the 
whole is the fum of the gravity of all its parts. 
Now, two bodies having an equal number of equal 
parts, if under the fame dimenfions there are no inter- 
vals deftitute of matter ; whence it follows, that as no 
portion of matter is fo fmall, but that body wherein 
it is contained may be wholly divided into parts 
equally fmall, there can be no reafon for the defcent 
of thefe, which will not hold equally for the defcent 
of that. 
Hence it may be concluded, that thofe bodies which 
do not equally gravitate under the fame dimenfions, 
do not contain the fame equal portions of matter, and 
therefore when we fee, that a cube of gold fubfides in 
water, at the fame time that an equal bulk of cork 
fwims upon it, it is evident, that the gold muft have 
a greater number of equal parts of matter under the 
fame bulk than the cork, or the cork muft have a 
greater number of vacuities than the gold, and that 
there are alfo in the water a greater number of vacui- 
ties than in the gold. 
Hence we have a clear idea both of denfity or gravity, 
and of Levity, and know, that in a ftridt fenfe the 
latter cannot be accounted any thing pofitive, but a 
mere negation, or abfence of body, which determines 
that body to be lighter than another which contains 
more matter. 
LICHEN. Liverwort. 
There being two forts of this plant which are ufed 
in medicine, and one of thofe being accounted a fo- 
vereign remedy for the bite of mad dogs, I thought it 
would not be improper to mention them here, though 
they are plants which cannot be propagated by any 
method, except by paring up the turf of Grafs 
whereon they grow, and laying it down on fome moift: 
fhady place, where, if the turf takes root, and 
thrives, the plants will fpread and do well. 
The two Sorts are, 
1. Lichen ( Petrous ) petrasus latifolius, five Hepa- 
tic a fontana. C. B.. P. Common broad-leaved Liverwort , 
2. Lichen ( Officinarum ) terreftris cinereus. Raft Syn, 
Aft- coloured Ground Liverwort . 
The firft fort grows on the fidesof wells, and in moift, 
lhady places, not only on the ground, but on ftones, 
bricksj or wood. Of this there are feveral varieties, 
7 Z yrhiclj 
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