occ 
lower the telescope to the horizon, in order 
to observe some point there in the centre 
of your glass, and that point is your meri- 
dian mark found by one observation only ; 
the best time for this operation is three 
hours before or three hours after twelve at 
noon. 2. To point the telescope on a 
star, though not on the meridian, in full day- 
light. Having elevated the equatorial cir- 
cle to the co-latitude of the place, and set 
the declination semi-circle to the star’s de- 
clination, move the index of the hour- 
circle till it shall point to the precise time 
at which the star is then distant from the 
meridian, found in tables of the right ascen- 
sion of the stars, and the star will then ap- 
pear in the glass. Besides these uses pecu- 
liar to this instrument, it is also applicable 
to all the purposes to which the principal 
astronomical instruments, viz. a transit, 
a quadrant, and an equal altitude instru- 
ment, are applied. See Vince’s “ Practical 
Astronomy.” 
OBSIDIAN, in mineralogy, a genus of 
the Pitch-stone family, found in nests in the 
pearl-stone of Hungary. It is common like- 
wise in Iceland, Siberia, the Levant islands, 
and in South America, and has obtained the 
name of the Iceland agate. The principal 
colour is velvet-black, but it passes into 
greenish grey. It is often striped and spot- 
ted. The specific gravity is about 2.4 : it 
melts into an opaque, grey mass. Speci- 
mens have been analysed, and found to con- 
tain 
Silica 
22 
Oxide of iron... 
too 
90 
Loss 
100 
It is on account of its great hardness and 
opaque blackness, and of its capability of re- 
ceiving a high polish, used as an ornament 
in dress. In Peru, before the conquest of 
the country by Spain, obsidian was used as 
a mirror, and in Europe it has been fashion- 
ed into reflectors for telescopes. 
OBTUSE, signifies blunt, dull, &c. in op- 
position to acute, sharp, &c. ; thus we say, 
obtuse angle, obtuse angled triangle, &c. 
OCCIDENT, in geography, the west- 
ward quarter of tlie horizon, or that part of 
the horizon where the ecliptic, or the sun 
therein, descends into the lower hemi- 
sphere, in contradistinction to orient. 
OCCIPITAL, in anatomy, a term appli- 
OCE 
ed to the parts of the occiput, or back part 
of the skull. 
OCCULT, something secret, hidden, or 
invisible. • The occult sciences are, magic, 
necromancy, cabbala, &c. 
Occult, in geometry, is used for a line 
that is scarcely perceivable, drawn witli the ' 
point of the compasses, or a leaden pencil. 
These lines are used in several operations, 
as the raising of plans, designs of building, 
pieces of perspective, &c. They are to be 
effaced when the work is finished. 
OCCULTATION, in astronomy, the 
time a star or planet is hidden from our sight, 
by the interposition of the body of the 
moon, or of some other planet. 
OccuLTATiON, Circle of perpetual, is a 
parallel in an oblique sphere, as far distant 
from the depressed pole, as the elevated 
pole is from the horizon. 
All the stars between this parallel and 
the depressed pole, never rise, but lie con- 
stantly hidden under the horizon of the 
place. 
OCCUPANCY, in law, is a right which 
one acquires to a thing by being the first to 
gain possession of it. But this right is now 
chiefly done away by the English law. For- 
merly, if a tenant for a term of another’s 
life died, leaving the cesfai que vie; that is, 
during the life of the person for whose life 
the estate was held ; be who first entered 
should hold the land during tlie other man’s 
life ; and he was in law called an occupant^ 
because his title was by his first occupa- 
tion. But now this title is prevented by 
the statutes 29 Charles II. c. 3, s. 12, and 
14 George II. c. 20, s. 9, which make the 
estate personal assets devisable, and charge- 
able with the debts of the deceased, in the 
hands of the heir, who enters as special oc- 
cupant. 
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. The Atlantic Ocean, which divides Eu- 
rope and Africa from America, which is ge- 
nerally about 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 In- 
dies from Africa, which is three thousand 
miles over. The other seas, which are 
called oceans, are only parts or branches of 
these, and usually receive their names from 
