GNO 
Gnomon, in geometry. If, in a parallel- 
ogram (PI. VI. Miscel. fig. 1.) the diameter, 
AC, be, drawn; also two lines, EF, HI, 
parallel to the sides of the parallelogram, 
and cutting the diameter in one and the 
same point, G, so that the parallelogram is, 
by these parallels, divided into four parallel- 
ograms, then are the two parallelograms, 
D G, B G, through which the diameter 
does not pass, called complements ; those 
through which the diameters pass, E H, 
FI, are called the parallelograms about 
the diameter; and a gnomon consists of the 
two complements, and either of the parallel- 
ograms about the diameter, viz, GD-f 
HE + El, orGD-j-FI + GB. 
Gnomon, in astronomy, a stile erected 
perpendicular to the horizon, in order to 
find the altitude of the sun. Thus, in the 
right angled triangle ABC, fig. 2, are given, 
A B, the length of the stile, B C, the length 
of its shadow, and the right angle, ABC. 
Hence, making, C B, the radius, we have 
this analogy for finding the angle, A C B, 
the sun’s altitude, viz. B C : A B : : radius : 
tangent of the angle C. 
By means of a gnomon, the sun’s meri- 
dian altitude, and consequently the lati- 
tude of the place, may be found more 
exactly than with the smaller quadrants. 
By the same instrument, the height of 
any object, G H, may be found ; for as, D F, 
fig. 3, the distance of the observer’s eye 
from the gnomon, is to, D E, the height ot 
the stile, so is, F H, the distance of the ob- 
server’s eye from the object to, G H, its 
height. 
The gnomon may be made useful in tak- 
ing the meridian altitude of the sun, and 
thence finding the latitude of the place. 
Having a meridian line drawn through the 
centre of the gnomon, mark the point where 
the shadow of the gnomon terminates when 
projected along the meridian line, and mea- 
sure the distance of that point from the cen- 
tre of the gnomon, which will be the length 
of its shadow ; then having the height of 
the gnomon, and the length of the shadow, 
the sun’s altitude is easily found. Thus, if 
A B be the gnomon, and A C the length of 
the shadow, then in the right angled trian- 
gle, ABC, we have A B and B C given ; 
hence the angle C is easily found, for C B : 
BA;: radius : tangent of the angle C ; that 
is, as the length of the shadow is to the 
height of the gnomon, so is radius to the 
tangent of the sun’s altitude above the 
horizon. Ex. We learn from Pliny, at the 
time of the equinoxes, that the shadow 
GNO 
was to the gnomon as 8:9, therefore w« 
say as 8 : 9 : : R : f = 1.123 the tangent of an 
angle of 48° 22', which is the height of the 
equator at Rome, and its complement 
41° 38' is therefore the height of the pole, 
or the latitude of the place. This method, 
however, requires correction for the sun’* 
parallax, and for refraction. 
GNOMONICS, the art of Dialing, 
which see. From the shadow of a rod, 
perpendicularly or obliquely placed on a 
plane, may be determined a triangle, by 
drawing from the top of the rod a line that 
shall touch the luminous body, forming 
with the rod the least possible angle. The 
sides of the triangle will be, first, the part 
of this line comprehended between the top 
of the rod and the given plane ; then the 
rod itself, and lastly, the line drawn from 
the bottom of the rod till it meets the other 
line already mentioned. This last line will 
be the shadow relatively to the given plane : 
it will increase and decrease in proportion 
as the sine of the angle, whose summit coin- 
cides with the summit of the rod, shall be 
greater or less, that is, in proportion as the 
luminous body shall descend or ascend with 
respect to the given plane ; and if that body 
move to the right or the left of the position 
first occupied by the triangle, that deter- 
mines the shadow, which will move on the 
plane in a contrary direction ; and on these 
principles the art of dialing consists. 
GNOSTICS, in church history, a sect of 
Christians so called from their pretensions 
to be more enlightened than others, and 
from their atfecting to be able to bring 
back mankind to the knowledge of the true 
God. The opinions held by these people 
have not been completely ascertained ; 
they were fond of speculation, and like 
many of the gnostics of modern times, held 
public worsliip and positive institutions in 
little esteem. 
GOAL, or Gaol. See Gaol. 
GOAT, in zoology. See Capra. These 
animals require scarcely any thing to keep 
them. Their milk is esteemed the greatest 
nourisher of all liquids, women’s milk ex- 
cepted, and very comfortable to the sto- 
mach. The young kids also are very good 
for the table, and may be managed in all re- 
spects like lambs. 
Goat’s beard, in botany. See Trago- 
pogon. 
Goat sucker. See Caprimulgus. These 
birds are. regarded by the American Indi- 
ans as very ominous. They believe that 
goat-suckers weie uot known in their coon- 
