a 
OVA 
OUA-CONG-YN, a town of Thibet; 32 miles S.W. 
of Hami. 
OUADA, or Goa, a town of the Ligurian republic, 
on the borders of France; 18 miles N.N.W. of Genoa 
OUAGIK, a town of Afiatic Turkey, in Natolia; 3 
miles S. of Ifmid. 
OUAIS’s Bay, a bay on the N. coaft of the ifland of 
cape Breton, in the gulf of St. Lawrence. 
» in Geometry, a curve refembling the contour of 
an egg, whence its name. The proper oval, or egg-fhape, 
is an irregular figure, being narrower at one end than it is 
-at the other; that is, the extreme breadth is not in the 
middle of its length. Ia this it differs from the ellipfis, 
which is the mathematical oval, and is equally broad at 
both ends. 
the common acceptation of the word the two curves 
tangents to the arcs, and as it does not in appearance 
differ from an ellipfis, is by artificers called an oval. 
= 
Mm 
about the centres F and L, with the diftances A F, L B, de- 
{cribe two {mall arcs M AN,A 3; which will form the 
ends of the curve ; and about the centres K and I, with the 
diftance I N, defcribe two arcs N ‘ » and the oval 
required will be defcribed. This curve, though it is called 
an oval, differs both from the true ellipfis, produced by the 
oblique fe€tion of a cone or cylinder, and alfo from the oval 
or egg-fhape figure, which is broader at one end than at the 
other: in fact, it is nothing more than fegments of different 
circles combined into one curve, which rather imitates the 
ellipfis than the oval, its ends being fimilar. 
The egg-fhaped curve may be defcnibed by means of an 
inftrument which has of late been produced with the inten- 
tion of defcribing ellipfes, though for this purpofe it is in- 
applicable: the principle of its ation is explained by fig. 2. 
Plate TI. In this, fuppofe A B an inflexible right line or 
ruler, the end B connedted by a joint to a crank C, which 
ght groove, its direction being in 
: this groove confines the end B to 
move in a right line tending to the centre of the circle, which 
the other end, A, defcribes when the crank is turned round. 
C; but the breadth will be diminifhed from this quantity, 
in the proportion of the parts of the lever AGB, con- 
Voi. XXV. 
OVA 
fidering the end A as its fulcrum, B the point where the 
action is applied, and G the point where the effe& is pro- 
duced. This reafoning is general, for if the tracing-point is 
confidered as removed to the point B, or within a very {mall 
: £ it, th 
& 
Mr. Wilfon Lowry, whofe pa accompany this 
work, has for fome years made ufe of a very perfeét and 
curious machine f i 
new conitruction, invented by Mr. rey, jun. from 
whofe drawings moft of the above fubje&ts are engraved. The 
Society of Arts have lately prefented the inventor with their 
gold medal for this inftrument, which 
3rft volume of their T'ranfaGtions. 
» by means 
of the pinion K, ufed to feparate their centres any required 
The circles have no central bar, but inftead thereof have 
two bars aa, aa, parallel to each other, and at fome diftance 
from the centre, leaving an open {pace between them, in 
which the drawing-pen or tracing-point is fituated: there 
are two crooked arms 4, 4, proceeding from the bars a, a, to 
the circular rim, to give it fufficient ftrength; and thefe 
being all the bars acrofs = circles, leave them very open 
4 to 
