OPT 
by ie the French by plut a Dieu ; and the Englifh by 
would to G 
In the a lanruawess fetting ear the adverb, the eae is 
the fame with the fubjunctive e inflexion of 
ora make what we call ae moods, being the Ge in 
“Indeed, in the Greek, the with is lane: by a particular 
inflexion, thence called optative ; and in the French, Spanifh, 
and Italian, there is fomething I like it ; pee ee ie 
ferving the fame purpofe. t the optative mood may be 
fafely retrenched from the Tica ‘and Englifh. pe sooner 
RIA, formed from orroua, J fee, among the 
Ancients, prefents made to a child the firlt a a perfon 
faw it. 
Opteria was alfo ufed for the prefents which | sia 
groom made his bride when fhe was condudted to him; 
this being the firft time he faw her. See Barthol. a Paes 
vet. 
PTIC, or Opricat, fomething that relates to vifon, or 
the es of feeing. 
1c Angle. 
ptic Axis. See Axis. 
Optic Chamber. See sea A Obfcur 
O 
ura. 
und either concave or gonvex 
ee VISIO 
See ANGLE 
For the manner of grinding and polifhing optic glaffes; fee 
Grinpine, Poxisuinc, Grass, &c. For their phenomena, 
fee Lens, Mirror, &c. 
The principal among optic glafles are telefcopes, mi- 
crofcopes, {petacles, reading glafles, magic lanterns, &c. 
See the conftru€tion and ufe of each under its proper ar- 
ticle, TELESCOPE, Micheeocs. eee Maacic Lan- 
fern, &C 
One or tia ee ged in Afronomy, is an Bouin 
irregularity in the of far diftant bodies called, 
ecawfe not really in ge moving bos ep ae from 
the eri of lie pectatar’s eye; at if the eye 
were in the centre, it would always fee the motions uni- 
The 0 optical inequality may be thus illuflrated: fuppofe a 
the ABDEFG 
body revolving in the periphery of a circle QP 
(Plate XV. Optics, fig. 22.) an - moving a sey 
arcs AB » DE, EF equal times; and f{ 
pofe the eye in the plane of the ue circle, cn at a dit 
tance from it, viewing the motion of the body bon O: 
when the body goes from A to B 
But in an equal time, while it 
moves through the arc BD, its apparent motion will be 
BOD, or the arc L M, which 
. And when arrived at 
D, it will be feen at the point M of the line NLM. But 
it ‘fpends the i time in defcribing DE, as it does ? 
AB or when arrived at E, it is ftill feen 
M:; appearing irene in all the {pace from D to . 
When it arrives at 
G, it will appear at _ fo it will feem h 
retrograde: and, ialtly, from Q to P, it will again cae 
sa nes 
10 Nore in Anatomy, the fecond pair of nerves, 
{prin ie om the crura of the medulla oblongata, and 
pafling fe to the eye. See Nervous Syfem. See alfo 
Vis 
Orne Nerves, Diminifoed Senfidility of. See Gutta 
2 CYENG. 
OPT 
Optic Pensil. See Penct of Raye 
Optic Place of a far, &c. “See P 
Optic Pyramid, in oo is Aa pyanid whofe bafe 
is ng vifible obje&, and its vertex in the eye; formed by 
s drawn fi a the feveral aia of the perimeter to the 
i. 
Hence alfo may appear what is meant by optic triangle. 
Optic Rays are ied nel ufed ow bani with which an 
optic pyramid, or optic triangle, is ter 
OPTICS, Optica, is properly dis ae of dire& vi- 
fron; which fee. 
Oprics is alfo ufed, in : larger fenfe, for the {cience of 
vifion, or vifibles in gener 
n which fenfe, optics clude alia and dioptrics < 
and even ‘ea seid which fee refpe& 
n its more extenfive pesca ge is a mixed ma. 
dicated eed which a aay the manner by which vifion 
is performed in the eye; 8 of fight in the general ; 
gives the reafons of the beveral modificstions or alte i 
which the - of light undergo in the eye; fhew 
why objects appear fometimes greater, fometimes fcnallers 
fometimes more diftin&, fometimes more confufed, fometimes 
nearer, and fometimes more remote. In this extenfi ive fig- 
nification, it is confidered ae fir Ifaac Newton in his ad- 
mirable work called ‘ Optics. 
Optics makes a confidersbl —_ of natural philofophy ; 
both as it explains the law a h 
vilion is performed; a ce as it ac coos 
phyfical phenomena, otherwife inexplicable. For what ‘can 
be determined about light, colours, oe opacity, 
meteors, the rainbow, parhelia, &c. but on se 
of optics ? What about the nature of the ftars ? F The ftru 
ture of the mundane fyftem ? The motions of the ae > 
The eclipfes of the ae haan &c. Optics, therefore, makes 
a oo a a aftronom 
een a a 
fimilar nature, which were clafled the rents under the 
— of meteors, though, i n fome refpects, blended 
with error, are neverthelefs, in ae refpecis, juft and 
t ceptionable and philofo- 
phicai account of = caufes that prod 
various circu faaice 
oe of the aaa inthis department of {cience was very 
aided with t 
It appears, that Ge ancient geometricians contented nae 
3P 2 8, 
