LEVEL. 
horny, with short jaws, the mandible thick, 
and three toothed at the tip; lip longer 
than the jaw, membranaceous and emargi- 
nate at the tip ; four feelers ; short, equal, 
filiform ; antennae short, clavate ; thorax 
with a long lanceolate scale beneath ; wings 
folded ; sting reflected, and concealed in a 
groove of the abdomen. There are four 
species, all foreign insects. 
LEVEL, an instrument constructed for 
the purpose of ascertaining the exact level 
of any fluid, building, &c. Of these there 
are two distinct kinds, viz. the horizontal, 
and the perpendicular : the first sort, which 
comprises spirit and air levels, is chiefly in 
use among surveyors; the latter is ordi- 
narily employed by artificers, and depends 
for exactness on a plumb line. 
The instruments used by persons taking 
the levels of lands, waters, &c. whereby to 
ascertain the comparative heights of dif- 
ferent spots, or tracts, are simple in the 
extreme, being generally made with a teles- 
cope of about fifteen inches long, fixed 
above a circular opening in a brass plate, 
so as to show a compass that traverses im- 
mediately below its centre, and gives not 
only the number of points, i. e. thirty-two, 
according to the mariner’s division, but by 
means of a neat brass rim, graduated with 
three hundred and sixty degrees, divided 
into thirty-six portions of ten degrees each, 
and numbered, shows the exact angle made 
between any two sights taken by the teles- 
cope, which traverses on two legs, support- 
ed in grooves on the outer edge of the brass 
plate, and allowing it to move round in a 
direction perfectly parallel thereto. The 
plane thus described by the circular motion 
of the telescope is made to correspond with 
that of the horizon by the aid of a small 
brass tube, about six or eight inches in 
length, fixed exactly parallel with the line 
of sight through the telescope, and screwed 
to its cylinder in such manner as to re- 
main firm. This little tube has on its 
upper side, or surface, an opening into 
which a piece of clear glass, corresponding 
with the cylindrical curve of the tube, is 
fitted and properly cemented. This piece 
of glass being perfectly centrical, serves to 
show how the fluid, generally alcohol (or 
pure spirits), with which the tube is filled, 
with the exception of a very minute por- 
tion, stand in respect of inclination with, 
or from the horizon. When the bubble of 
air left in the tube floats exactly centrical, 
in that portion which is covered with glass, 
the tube itself must be level ; and as it is 
affixed at an exact parallel with the line of 
sight, which passes through the axis, or 
centre of the telescope, from the eye to 
the crossing of two hairs, at right angles, 
within the telescope, the instrument itself 
must then be level, and that part of any 
object, however distinct, which is cut or 
indicated by the line of sight, is ascertain- 
ed by the centre of the cross made by the 
hairs being on a rectilinear level with the 
line of sight. But in consequence of the 
curvature of the earth’s surface, the horizon- 
tal level will be different from the recti- 
linear level, and will describe an arc paral- 
lel with the surface of the earth. This 
curvature amounts to about eight inches 
in every mile ; or, in more minute parts, 
may be taken at four and a half lines for 
every hundred yards. 
The usual mode of taking a level is by 
means of a painted board, about a foot 
square, having a broad white stripe drawn 
horizontally across its centre. This board 
slides up and down a long pole, which being 
held perpendicularly by an assistant, at any 
appointed spot of which the level is to be 
ascertained, the instrument is brought to 
file exact direction in which the pole is 
situated ; so that the latter may coincide, 
or as it is technically called, “ be in one" 
with that basis which is vertical within the 
tube. The legs on which the level is sup- 
ported, (generally the same as in theo- 
dolites, &c.) are spread so as to be firm- 
after bringing the compass as nearly as may 
be practicable to a level: by means of four 
screws, which serve to raise the different 
sides of the plate at pleasure, the utmost 
precision is attainable. The board is then 
moved up or down on the pole, which is 
marked all the way up in feet, inches, 
halves, and quarters, until the centre paint- 
ed line “ is in one” witli the horizontal 
hair within the telescope. The height of 
the telescope above the surface on which 
it stands must be deducted from the num- 
ber of feet and inches, at which the line 
on the board stands above the spot where 
the pole is fixed : the residue shows how 
much that is below the place where the 
instrument stands. But if the height of 
the line on the board be less than that at 
which the line of sight in the level stands 
from the ground, then the difference be- 
tween those two heights will exhibit how 
much the former is above the latter. 
By this simple mode the level of any 
intended land, &c. may be correctly taken, 
observing to limit the sight as much as 
