OBE 
they are used in Ireland, and in the Highlands 
of Scotland, to dye a dark brown or ches- 
nut colour ; this plant is a native ot most 
parts of Europe, in slow streams, pools and 
ditches, flowering in July and August. 
NYSSA in botany, a genus of the Poly- 
gamia Dioecia class and order. Natural 
order of Holoraceae. Elmagmi, Jussieu. 
Essential character : calyx, five parted ; co- 
rolla none : male, stamens ten : hermaphro- 
dite, stamens five ; pistil one ; drupe inferior. 
There are two species, viz. N. integrifolia, 
mountain tnpelo ; and N. denticulata, water 
tupelo ; the former of which grows natural- 
ly in Pennsylvania, rising to the height of 
thirty or forty feet, and nearly two in dia- 
meter, sending off many horizontal and 
often depending branches; leaves of a 
OBJ 
dark green colour on tlie upper surface, 
but lighter underneath; the flowers are 
produced upon long footstalks, from the 
base of the young shoots, dividing irregular- 
ly into several parts, each supporting a 
small flower ; the female trees have fewer 
flowers, produced upon much longer simple 
cylindrical footstalks. The Virginian water 
tupelo tree grows naturally in wet swamps, 
or near large rivers in Carolina and Florida, 
rising with a strong upright trunk to the 
height of eighty or an hundred feet, divid- 
ing into many branches towards the top ; 
the leaves are large, of an oval spear-shaped 
form; the berries are nearly the size and 
shape of small olives, and are preserved by 
the French inhabitants upon the Missisippi, 
where it abounds, and is called the olive tree. 
o. 
O or o, the fourteenth letter, and 
9 fourth vowel of our alphabet, pro- 
nounced as in the words nose, rose, See. 
The sound of this letter is often so soft, 
as to require it double, and that chiefly in 
the middle of words ; as goose, reproof, &c. 
and in some words tliis oo is pronounced 
like u short, as in flood, blood. Sec. 
As a numeral, O is sometimes used ^ 
eleven ; and with a dash over it, thus O, 
for eleven thousand. 
In music, the O, or rather a circle, or 
double CO) 
a semi breve ; and, by the Italians, circolo. 
The O is also used as a mark of ti iple time, 
as being tlie most perfect of all figures. 
See Triple. 
OAK. See Quercbs. 
OAKUM, old ropes untwisted, and pull- 
ed out into loose hemp, in order to be used 
in caulking the seams, tree nails and bends 
of a ship, for stopping or preventing leaks. 
OAR, in navigation, a long piece of 
wood, made round where it is to be lield in 
the hand, and thin and broad at the other 
end, for the easier cutting and resisting the 
water, and consequently moving the vessel, 
by rowing. 
OAT. See Avena. 
OBELISK, in architecture, a truncated, 
quadrangular, and slender pyramid, raised 
as an ornament, and frequently charged 
either with inscriptions or hieroglyphics. 
OBJECT, in philosophy, something ap- 
prehended, or presented to the mind, by 
sensation or by imagination. 
Object glass of a telescope, or microscope, 
the glass placed at the end of the tube 
which is next the object. 
To prove the goodness and regularity of 
an object-glass, on a paper, describe two 
concentric circles, the one having its diame- 
ter the same with the breadth of the object- 
glass, and the other half that diameter ; di- 
vide the smaller circumference into six 
equal parts, pricking the points of division 
through with a fine needle ; cover one side 
of the glass with this paper, and, exposing 
it to the sun, receive the rays through these 
six holes upon a plane ; then by moving the 
plane nearer to, or fiirther from the glass, it 
will be found whether the six rays unite 
exactly together at any distance from the 
glass ; if they do, it is a proof of the regula- 
rity and just form of the glass ; and the said 
distance is also tlie focal distance of tlie 
glass. A good way of proving the excel- 
lency of an object-glass, is by placing it in 
a tube, and trying it with small eye-glasses, 
at several distant objects ; for that object- 
glass is always the best which represents 
