LEVEL. 
<53 
zontal line by means of a surface of water or 
other fluid, founded on this principle, that 
water always places itself level or horizontal. 
The most simple kind is made of a long 
wooden trough or canal, which being equally 
filled with water, its surface shews the line of 
level. 
'The water-level is also made with two cups 
fitted to the two ends of a straight pipe, about 
an inch diameter, and three or four feet long, 
by means of which the water communicates 
from the one cup to the other; and this pipe 
being moveable on its stand by means of a 
ball and socket, when the two cups shew 
equally full of water, their two surfaces mark 
the line of level. 
T his instrument, instead of cups, may also 
be made with two short cylinders of glass 
three or four inches long, fastened to each 
extremity of the pipe with wax or mastic. 
The pipe is filled with common or coloured 
water, which shews itself through the cylin- 
ders, by means of which the line of level is 
determined; the height of the water, with 
respect to the centre of the earth, being al- 
ways the same in both cylinders. This level, 
though very simple, is yet very commodious 
for levelling small distances. 
^t-Level, that which shews the line of 
level by means of a bubble of air inclosed 
with some iluid in a glass tube of an indeter- 
minate length and thickness, and having its 
two ends hermetically sealed. When the 
bubble fixes itself at a certain mark, made 
exactly in the middle of the tube, the case or 
ruler in which it is fixed is then level. V hen 
it is not level, the bubble will rise to one end. 
This glass tube may be set in another of 
brass, having an aperture in the middle, 
where the bubble of air may be observed. It 
should be filled with a liquid not liable to 
freeze nor evaporate. 
There is one of these instruments with 
sights, being an improvement upon that last 
described, which, by the addition of other 
apparatus, becomes more exact and commo- 
dious. It consists of an air-level (Plate 
Miscel. fig- !4t>) about eight inches long, 
and about two-thirds, of an inch in diameter, 
set in a brass tube 2, having an aperture in 
the middle C. The tubes are carried in a 
straight ruler, of a foot long; at the ends of 
which are fixed two sights 3, 3, exactly per- 
pendicular to the tubes, and of an equal 
height, having a square hole, formed by two 
fillets of brass crossing each other at right 
angles; in the middle of this is drilled a 
very small hole, through which a point on a 
level with the instrument is seen. The brass 
tube is fastened to the ruler by means of two 
screws; the one of which, marked 4, serves 
to raise or depress tire tube at pleasure, for 
bringing it towards a level. The top of the 
ball and socket is rivetted to a small ruler 
that springs, one end of which is fastened 
with springs to. the great ruler, and at the 
other end is a screw 5, serving to raise and 
depress the instrument when nearly level. 
But this instrument is. still less commodious 
than the following one: for though the holes 
are ever so small, yet they will still take in 
too great a space to determine the point of 
level precisely. 
Fig. T 47. is a level with telescopic sights, 
first invented by Mr. Huygens. It is like 
tire last, with this difference, that instead of 
plain sights it carries a telescope to deter- 
mine exactly a point of level at a consider- 
able distance, 'the screw 3, is for raising or 
lowering a little fork for carrying the hair, 
and making it agree with the bubble of air 
when the instrument is level ; and the screw 
4 is for making the bubble of air, D or E, 
agree with the telescope. The whole is fit- 
ted to a ball and socket, or otherwise moved 
by joints and screws. It may be observed, 
that a telescope may be added to any kind ot 
level, by applying it upon, or parallel to, the 
base or ruler, when there is occasion to take 
the level af remote objects ; and it possesses 
this advantage, that it may be inverted by 
turning the ruler and telescope half-round ; 
and if then the hair cut the same point that it- 
did before, the operation is just. Many va- 
rieties and improvements of this instrument 
have been made by the more modern opti- 
cians. 
Dr. Desaguliers proposed a machine for 
taking the difference of level, which contain- 
ed the principles both of a barometer and 
thermometer; but it is not accurate in prac- 
tice. 
Reflecting Level, that made by means of 
a pretty long surface of- water, representing 
the same object inverted, which we see erect 
by the eye; so that the point where these 
two objects appear to meet, is on a level with 
the place where the surface of the water is 
found. 
There is another reflecting level, consist- 
ing of a polished metal mirror, placed a 
little before the object-glass of a telescope, 
suspended perpendicularly. This mirror 
must be set at an angle of 45 degrees ; in 
which case the perpendicular line of the te- 
lescope becomes a horizontal line, or a line 
of level : which is the invention of M. Cas- 
sini. 
Artillery AooTLevel, is in form of a 
square (fig. 148.), having its two legs or 
branches of an equal length ; at the junction 
of which is a small hole, by which hangs a 
plummet playing on a perpendicular line in 
the middle of a quadrant, which is divided 
both ways from that point into 45 degrees. 
This instrument may be used on other oc- 
casions by placing the ends of its two branches 
on a plane ; for when the plummet plays per- 
pendicularly over the middle division of the 
quadrant, the plane is then level. 
To use it in gunnery, place the two ends 
on the piece of artillery, which may be raised 
to any proposed height by means of the plum- 
met, which will cut the degree above the le- 
vel. But this supposes the outside of the 
cannon is parallel to its axis, which is not 
always the case ; and therefore they use ano- 
ther instrument now, either to set the piece 
level, or elevate it at any angle; namely a 
small quadrant, with one of its radii conti- 
nued out pretty long, which being put into 
the inside of the cylindrical bore, the plum- 
met shews the angle of elevation, or the line 
of level. 
. Carpenter's , Bricklqyer's, or Pavior's Le- 
vel, consists of a long ruler, in the middle of 
which is fitted at l ight angles another broader 
piece, at the top ot which is fastened a plum- 
met, which when it hangs over the middle 
line of the second or upright piece, shews 
that the base or long ruler is horizontal or 
level. Fig. 149. 
Mason's Level, is composed of three 
rulers, so jointed as to form an isosceles tri- 
angle, somewhat like a Roman A; from the 
vertex of which is suspended a plummet, 
which hangs directly over a mark in the 
middle of the base, when this is horizontal or 
level. 
Phan or Pendulum Level, said to be in- 
vented by M. Picard, fig. 150. This shews 
the horizontal line by means of another line 
perpendicular to that described by a plum- 
met or pendulum. T his level consists of 
two legs or branches, joined at right angles* 
the one of which, of about IS inches long, 
carries a thread and plummet; the thread 
being hung near the top of the branch, at the 
point 2. T lie middle of the branch where 
the thread passes is hollow, so that it may 
hang free every where: but towards the 
bottom, where there is a small blade of sil- 
ver, on which a line is drawn perpendicular 
to the telescope, the said cavity is covered 
by two pieces of brass, with a piece of glass 
G, to see the plummet through, forming a 
kind of case, to prevent the wind horn agi- 
tating the thread. T he telescope, of a pro- 
per length, is fixGljLo the other leg of the in- 
strument, at right angles to the perpendicu- 
lar, and having a hair stretched horizontally 
across the focus of the object-glass, which 
determines the point of level, when the string 
of the plummet hangs against the line on the 
silver blade. The whole is fixed by a ball 
and socket th its stand. 
Fig. 1 5 1 . is a Balance Level, which being 
suspended by the ring, the two sights, when 
in eqnilibrio, will be horizontal, or in a level. 
But the most complete level is the Spirits 
Level, invented by the late Mr. Ramsden. 
See Plate Spirits Level. ABD, fig. 7. are 
the three legs upon which it is placed ; when 
shut up, they form one round rod, and are 
kept together by three ring's: these legs are 
jointed to a brass frame E, on the top of 
which is a male screw, screwing into a female 
screw within the projection a of the plate F. 
Within the top of a, figs. 4 and 7, is a he- 
mispherical cavity to contain the spherical 
ball, fig. 5: this ball has a male screw d on 
its top, which screws into a female screw b, 
fig. G, in the plate G, fig. 7 and fig. 6, the 
ball is put up through anopenlngr, fig. 4, and 
screwed to the plate, fig. G ; so that the upper 
plate G can move in any direction within 
certain limits by the play of the ball in its 
socket; to confine the upper plate G when it 
is set in anv direction, four screws, HlillH, 
figs. 4 and 7,. are employed; they work in 
tubes firmly fixed to the plate F, and are 
turned by their milled heads; the upper ends, 
of these screws act against the under side of 
the plate, fig.. 6, as shewn in fig. 7 ; so that 
when, the plate G is required to be moved in 
any direction, it is done by screwing up one 
screw and screwing down the opposite till it 
is brought to the proper inclination ; then by 
screwing up both together, the plate is firmly 
fixed. The ball, fig. 5, has a conical hole f 
through it, to receive an axis which is screwed 
fast to the bottom of the compass-box I, fig. 
7 ; a screw screwed into the end of this axis 
prevents its being lifted out, and at the same 
time leaves- it at liberty to turn round inde- 
pendant of the ball, fig. 5. On each side of 
the compass-box I, is a bar KK, on the end 
of which are fixed two forked pieces 10, 
called the Y’s (from their resemblance to 
that letter), carrying the telescope M. One 
of these (6) is capable of being raised or 
