O C I 
285 
OCEAN, in geography, that vast collec- 
tion of salt and navigable waters, in which 
the two continents, the first including Eu- 
rope, Asia, and Africa, and the last Ame- 
rica, are inclosed like islands. The ocean is 
distinguished into three grand divisions: 1. 
T he Atlantic ocean, which -divides Europe 
and Africa from America, which is generally 
abty.it three thousand miles wide ; 2. The 
Pacific ocean, or South-sea, which divides 
America from Asia, and is generally about 
ten thousand miles over; and.. 3. The Indian 
ocean, which separates the East Indies from 
Africa, which is three thousand yules over. 
The other seas which are called oceans, are 
only parts or branches of these, and usually 
receive their names from the countries they 
border upon. 
OC H N A, a genus of the monogynia order, 
in the p Ivandria class of plants; and in the 
•natural method ranking with those of which 
the order is doubtful. The corolla is pentu- 
petalous; the calyx pentaphyllous; the ber- 
ries monospermous, and affixed to a large 
roundish receptacle. There are three spe- 
cies, trees of the East Indies and South 
America. 
OCHRE, in natural history, a genus of 
earths, slightly coherent, and composed of 
fine, smooth, soft, argillaceous particles, 
rough to the touch, and readily diffusible in 
water. It is a combination of alumina and 
red oxide of iron. Ochres are of various co- 
lours, as red, blue, yellow, brown, green, 
&c. 
OCHROMA, a genus of the pentandria 
order, in the monadelphia class of plants; 
and in the natural method ranking under the 
37th order, columntferx. The corolla con- 
sists of six petals, three of which are external, 
and the other three internal; the anthers 
unite, and form a spiral pillar round the style ; 
the capsule is long, and has five loculaments, 
which contain a number of black round seeds. 
Of this there is only one species, viz. the 
ochroma lagopus, the down-tree, or cork- 
wood. This tree is frequent in Jamaica, is 
of speedy growth, and rises to about 23 or 
30 feet. The flowers are large and yellow. 
The capsules are about five inches long, 
rounded, and covered with a thin skin; which 
when dry fails off in five longitudinal seg- 
ments, and leaves the fruit greatly resem- 
bling a hare’s foot. The down is short, soft, 
and silky; it is used sometimes to stuff beds 
and pillows ; but, like other vegetable downs, 
is apt to get into clots: an insipid dear gum 
exudes from the tree when wounded. T he 
bark is tough, and its fibres are in a reticu- 
lated form ; it might be made into ropes. 
The dried wood is so very light and buoyant, 
as to be used by the fishermen in Jamaica for 
their -nets instead of pieces of cork. 
OCHROXYLUM, a genus of the class 
and order pentandria trigynia. '1 he calyx 
is five-cleft; petals five; nect. angular, three- 
Iobed, gland. ; capsules three, approximate- 
ly, one-celled, two-seeded. 
OCIMUM, or Ocymum, basil, a genus 
of the didynamia gymnospermia class of 
plants, with a bilabiated cup ; its flower is 
monopetalous and ringent ; and its seeds, 
which are four in number, are contained in 
the cup, which closes for that purpose. 
There are 25 species. Both the herbs and 
seed of basil are used iu medicine, and are 
ODO 
said to be good in disorders of the lungs, and 
to promote the menses. 
OCTAGON, or Octogon, in geometry, 
is a figure of eight sides and angles ; and this, 
when all the sides and angles are equal, is 
called a regular octagon, or one which may 
be inscribed in a circle. It the radius of a 
circle circumscribing a regular octagon is 
= r, and the side of the octagon — y ; then 
y — -y/ 2r ' — r \/2 r : . 
Octagon, in fortification, denotes a place 
that has eight bastions. 
OCTAHEDRON, or Octaf.dron, in 
geometry, one of the five regular bodies, con- 
sisting ot eight equal and equilateral triangles. 
The square of the side of the octahedron 
is to the square of the diameter of the circum- 
scribing sjdiere, as 1 to 2. If the diameter 
of the sphere is 2, the solidity of the octa- 
hedron inscribed in it will be 1,33333 nearly. 
The octahedron is two pyramids put to- 
gether at their bases ; therefore its solidity 
may be found by multiplying the quadrangu- 
lar base of either of them, by one third of the 
perpendicular height of one ol them, and 
then doubling the product. 
OCTAND RIA, the eighth class in Lin- 
naeus’s sexual system ; consisting of plants 
with hermaphrodite flowers, which are fur- 
nished with eight stamina, or male organs of 
generation, bee Botan y . 
OCTANT, or Octile, in astronomy, 
that aspect of two planets, wherein they are 
distant an eighth part of a circle, or 45°, from 
each other. 
OCTAVE, in music, an interval contain- 
ing seven degrees, or twelve semitones, and 
which is the tirst of the consonances in the 
order of generation. The most simple per- 
ception that we can have of two sounds is that 
of unisons, which, resulting from equal vi- 
brations, are as one to one; the next to this 
in simplicity is the octave, which is in double 
computation as one to two. The harmonies 
of these sounds have a perfect agreement, 
which distinguishes them from any other in- 
terval, and contributes to give them that uni- 
sonous effect which induces the common ear 
to confound them, and take them indiffe- 
rently one for the other. This interval is 
called an octave, because moving diatoni- 
cally from one term to the other, we produce 
eight different sounds. The octave compre- 
hends all the primitive and original sounds; 
so that having established a system, or scries 
of sounds, in the extent of an octave, we can 
only prolong that series by repeating the 
same order in a second octave, and again in 
a third, and so on, in all which we shall not 
And any sound that is not the replicate of 
some sound in the adjoining octave. 
The complete and rigorous system of the 
octave requires three major tone’s, two minor, 
and two major semitones. The temperatecl 
system is of five equal tones, and two semi- 
tones, forming together seven diatonic de- 
fff665. 
° ODE. See Poetry. 
ODONTOGNATHUS, a genus of fishes 
of the order apodes. The generic character 
is, mouth furnished with a strong moveable 
lamina or process on each side the upper 
jaw; gill membrane five-rayed. 
Aculeated odontognathus. The genus 
odontognathus cofisists of a single species, of 
OEN 
which the following is the description. T he 
head, body, and tail, are very compressed; 
the lower jaw, which is longer than the 
upper, is very nXich elevated towards the 
other when the mouth is closed, insomuch as 
to appear almost vertical; and is lowered 
somewhat in the manner of a drawbridge 
when the mouth is opened, when it appears 
like a small scaly boat, very transparent, fur- 
rowed beneath, and finely denticulated on the 
margins; this lower jaw, in the act ot de- 
pression, draws forwards two flat, irregular 
laminae, of a scaly substance, a little bent at 
their posterior end, and larger at their origin 
than at their tips, denticulated on their an- 
terior margin, and attached, one on one side 
and the other on the opposite, to the most 
prominent part of the upper jaw ; when the 
mouth is closed again, these pieces apply 
themselves on each side to one ot the oper- 
c. ula, of which they represent the exterior 
denticulated border; in the middle of these 
jaws is placed the tongue, which is pointed 
and free in its movements; the gill-covers, 
which are composed of several pieces, _are 
very transparent at the hind part, but scaly 
and’ of a bright silver-colour in front ; the 
gi 1-membrane is also silvery, and has five 
rays; the breast is terminated below by a 
sharp carina furnished with eight crooked 
spines; the carina of the belly is also furnish- 
ed with twenty-eight spines, disposed in two 
longitudinal range's ; the anal fin is very long, 
and extends almost as far as the base of the 
tail-fin, which is of a forked shape; the dor- 
sal fin is placed on the tail, properly speak- 
ing, at about three quarters ot the whole 
length of the animal, but it is extremely 
small. T he general length of this fi-h is 
three decimetres, and its colour, so far as may 
be conjectured from specimens preserved 
for some time in spirits, is a bright silver. It 
is a native of the American seas, and is com- 
mon about the coasts of Cayenne, where it 
ranks in the number of edible fishes. 
O ECONOMY, animal, comprehends flic 
various operations of nature, in the gem ra- 
tion, nutrition, and preservation of animals. 
See Anatomy, Physiology, Compara- 
tive Anatomy, Digestion, &c. 
OEDEMA. See Surgery. 
OEDF.RA, a genus of the syngenesia polv- 
gamia-segregata class and order; the calyx 
many-flowered ; corollets tubular, hermaphro- 
d. te, with one or two female ligulale florets : 
repep. chaffy, down of several chaffs. There 
are two species, herbs of the Cape. 
OENANTUE, water (or hemlock) drop- 
wort: a genus of the digynia order, in the 
pentandria class of plants; and in the natural 
method ranking under the 45th order, imi- 
beHatie 'Die florets are difform ; those of 
the disc, sessile and barren ; the fruit Crowned 
with the calyx. Tnere are 1 1 species, of 
which the most remarkable is the crocata, 
or hemlock dropwort, growing frequently 
the banks of ditches, rivers, and lakes, in 
many parts of Britain. The root and leaves 
of this plant are a strong poison ; several 
persons have perished by eating it through 
mistake, either for water-parsnips or for ce- 
lery, which last it much resembles in its 
leaves. So exceedingly deleterious is this 
plant, that Mr. Lightfoot tells hs he has- 
heard the late Mr. Christopher d’Ehret, the 
celebrated botanic painter say, that while he 
