ORB 
proper use of the same instrument every 
purpose of the pentagraph may also be 
answered ; as a painting may be reduced 
in any proportion required, by placing it at 
a distance in due proportion greater than 
that of the paper from the instrument. In 
this case a lens becomes requisite for 
enabling the eye to see at two unequal dis- 
tances with equal distinctness ; and in order 
that one lens may suit for all these pur- 
poses, the»e is an advantage in varying the 
height of the stand according to the propor- 
tion in which tire reduction is to be ef- 
fected. 
OPTION, in law, every bishop, whether 
created or Iranslated, is bound immediately 
after confirmation, to make a legal convey- 
ance to the archbishop, of the next avoid- 
ance of such dignity or benefice belonging 
to the see, as the said archbishop shall 
choose, which is therefore called an op- 
tion. 
OR, in heraldry, denotes yellow, or gold 
colour. In the coats of noblemen it is bla- 
zoned topaz; and in those of sovereign 
princes, sol. It is represented in engraving 
by small points or dots, scattered all over 
the field or bearing. 
ORATORIO, in music, a species of mu- 
sical drama, originally an imitation of the 
serious opera, the subject of which is gene- 
rally taken from scripture, and can be only 
treated properly by music of the sublimest 
style. 
ORBIT, in astronomy, the path of a pla- 
net or comet, or the curve that it describes 
in its revolution round its central body : thus 
the Earth’s orbit is the curve which it de- 
scribes in its annual course, and usually 
called the ecliptic. The orbits of all the 
planets are ellipses having the Sun* in 
their common focus ; in which curve they 
move according to an invariable law. See 
Astronomy. However, the orbit of the 
Earth is considerably disfigured by the 
action of tlie Moon; as is also the orbit 
of Saturn by the action of Jupiter, when 
they happen to be in conjunction. Though 
the orbits of the planets be elliptical, 
not circular, yet that they are very little 
so, even in the most eccentric orbit, as 
that of Mercury, will appear by comparing 
their Eccentricities with their mean dis- 
tances from the Sun, The orbits of the pla- 
nets are not all in the same plane with the 
ecliptic, but are variously inclined to it, and 
to each other; but still the plane of the 
ecliptic intersects the plane of the orbit of 
every other planet, in a right line which 
ORC 
passes through the Sun, called the line of 
the nodes, and the points of intersection of 
the orbits themselves ai-e called the nodes. 
ORCHESTRA, in music, that enclosed 
part of the theatre between the audience 
and the curtain; in which the instrumental 
performers sit. 
ORCHIDE.E, in botany, the seventh 
order in Linnaeus’s Fragments of a Natural 
Metliod, consisting of Orchis, and the plants 
that resemble it in habit, powers, and sen- 
sible qualities. The flowers are herma- 
phrodite, and placed at the summit of the 
stalk, either in a spike, or in a panicle. 
Each flower is accompanied with a leaf that 
is smaller than the other leaves, and forms 
a sort of sheath round the stalk. The petals 
are five in number, and very irregular. The 
flowers of the difierent species are remark- 
ably various and singular in their shape, 
resembling different kinds of animals or 
insects. 
ORCHIS, in botany, a genus of the Gy- 
nandria Diandria class and order. Natural 
order of Orchideae. Essential character; 
nectary a horn or spur behind the flower. 
There are fifty species. Among which we 
shall notice the O. bifolia, butterfly orchis. 
This plant has ovate bulbs, tapering to a 
point at the base ; thick fleshy fibres pro- 
ceed above them from the base of the stem; 
one of these bulbs is always wrinkled and 
withered, whilst the other is plump and de- 
licate; the first is the parent of the actual 
stem ; the second is an offset, from the 
centre of which the stem of the succeeding 
year is destined to arise. Such are the 
means that nature uses, not only to disse- 
minate plants, but to enable them to change 
their place, and thus to draw in fresh nutri- 
ment. The second root is always about 
half an inch from the centre of the first, so 
that in twenty years tlie plant will have 
marched ten inches from the place of its 
birth. This mode of increase is particularly 
necessary in a family of plants that rises 
with great difficulty, and very seldom by 
seed. O. conopsea, long-spurred Orchis, is 
distinguished by the remoteness of the cells 
or cases in which the stamens are lodged, 
and again by the colour of the corolla, the 
great length of the spur, the delicious fra- 
grance of its flowers, vying with that of the 
honeysuckle, and particularly by the un- 
usual structure of its flowers. Below the 
stigma, which is remarkably well defined 
in this species, there is a circular opening 
between the cavities containing the sta- 
mens; just above the stigma is a very con- 
