842 
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of the books then in the library. Thofe fix books, with 
the imperfett feventh, were firft publifhed at Bafil, by 
Xylander, in 1575, but in a Latin verfion only, accompa¬ 
nied with the Greek fcholia of Maximus Planudes upon 
the firft two books, and obfervations of his own. After¬ 
wards a new edition of them was publifhed at Paris, in 
Greek and Latin, in 1621, by the learned and ingenious 
M. Bachet de Meziriac. In 1670 another edition of them 
W'as publifhed at Touloufe, with the additional notes of 
the profound mathematician M. de Fermat. 
DIOP'SIS, f. the Spectacle Fly ; in entomology, 
a genus belonging to the order of diptera ; the character 
of which is : eyes placed at the extremity of two horns. 
For the difcovery of this genus we are indebted to Dr. 
Fothergill, who prefented his friend fir Charles Linnaeus 
with a great number of infects that lie had collected from 
South America and Guinea; among which, in arranging 
them, M. Dahl found this Angular fly, of which he pub- 
lifhed an account in his Dijfcrtatio Entomologica, 4to. Upfal, 
1775. There never has been any other fpeciesdifcovered 
befides this one, which Linnaeus named as follows : 
Diopfis ichneumonea, the ichneumon fpe<Stacle-fly : it 
is about the fize of the red ant, and height of the com¬ 
mon ichneumon-fly. It has one tooth in the mouth on 
each fide; the head, which is of a reddilh colour, is 
lengthened, and from which proceed two filiform horns, 
as long as the corfelet ; thefe horns are divergent, folid, 
inarticulate, and ferruginous; and at the tops or ends of 
thefe are placed the eyes, which are fpherical, inclined, 
and lucid black. Juft below them, on the inner part of 
each horn, is a tubercle, whence iffues a kind of bridle, 
which feems to be the rudiment of an antenna. The 
corfelet is black, armed with a fingle fpine on eacli fide, 
and terminated by two ye!low r fubulated fpines. It has a 
pair of tranfparent hyaline wings, with a black fpot on 
the outer part of each, near the end. The body is red- 
difli; legs yellow; belly like the ichneumon, club-fltaped, 
fomewhat pedicelled, the two lad wings black ; feet 
black; front thighs club-fhaped. It was for fome time 
difficult to decide in what order this lingular infeft fhonld 
be placed. The dyle and club-fhaped balancers under 
their fcales at length determined Gtnel-in to place it 
among the diptera: yet the fpines on the corfelet diftin- 
guifh it from all the genera of that order, and make it 
approach to the ants. Its long claws and club-diaped 
belly, and black fpot towards the extremity of the wings, 
give it the air of an ichneumon; from which however it 
is clearly didinguifhed by the horns being immoveable, 
whereas thofe of the ichneumon are in continual motion ; 
they are not jointed, are much longer than the head, cy¬ 
lindrical, and firmly dxed, and cannot therefore be re¬ 
garded as antennae. The eyes are very remarkably placed 
at the extremity of the horns, fomewhat prominent, and 
therefore very far from the head. The antennae are not 
difcovered at firft fight; but, by dole attention, the tu¬ 
bercles above-mentioned are feen near each eye, furnifhed 
with a bridle or hair; and thefe no doubt perform the 
office of antennas. In the correfpondent engraving, we 
have given a corref! figure of this curious infeft, taken 
from the fly itfelf, by Ftiefsly. 
DIOP'TER, f. The index or alhidade of an aftrolabe, 
or other fuch indrument. 
DIOP'TRA,y. A mathematical indrument invented 
by Hipparchus, which ferved for feveral ufes ; as, to le¬ 
vel water-courfes ; to take the height of towers, or places 
at a didance; to determine the places, magnitudes, and 
didances, of the planets, &c. Alfo a furgical indrument 
for dilating any natural cavity when difeafed, the better 
to afcertain its date. 
DIGP'TRIC, or Dioptrical, f. [3W%/2ai, Gr.] 
Affording a medium for the fight; afiiding the fight in 
the view of didant objects.—View the afperities of the 
moon through a dioptric glafs, and venture at the propor¬ 
tion of her hills by t their fhadows. Afore.—Being excel- 
D I O 
lently well furnifhed with dioptrical glafles, he had not 
been able to fee the fun fpotted. Boyle. 
DIOP'L RICS, f. [S'lOTrlgiy.n, of h,o7p.ofi.a.i, Gr. to look 
through.] The fcience of refrafted vifion ; or that part 
of optics which explains the effefts of light as refratled 
by pafling through different mediums, fuch as air, water, 
glafs, &c. and efpecially lenfes. Dioptrics is confelfedly 
one of the mod ufeful and pleafant of all the human 
fciences ; bringing the remoted objects near to view ; en¬ 
larging the fmalled objedts fo as to diew their minute 
parts ; and even, as it were, giving fight to the blind ; 
and all this by the Ample means of the attractive power 
in glafs and water, which caufes the rays of light in their 
paflage through them to alter their courfe according to 
the different fubdances of the medium ; whence it hap¬ 
pens, that the objedts viewed through them, do, in ap¬ 
pearance, alter their magnitude, didance, and fituation. 
The ancients have treated of diredt and refledted vi- 
fion ; but what they have written of refradted vifion, is 
very imperfedt. J. Baptida Porta wrote a treatifeon re- 
fradtion, in nine books, but wi bout any great improve¬ 
ment. Kepler was the fird who fucceeded in any great 
degree, on this fubjedt ; having demondrated the pro¬ 
perties of fpherical lenfes very accurately, in a treatife 
fird publifhed in 1611. After Kepler, Galileo gave 
fomewhat of this dodlrine in his Letters ; as alfo an Ex¬ 
amination of the Preface of Johannes Pena upon Euclid’s 
Optics, concerning the ufe of optics in adronomy. Des 
Cartes alfo wrote a treatife on Dioptrics, commonly an¬ 
nexed to his Principles of Philofophy, which is one of 
his bed works ; in which the true manner of vifion is 
more didindtly explained than by any former writer, and 
in which is contained the true law of refradfion, which 
was found out by Snell, though the name of the inventer 
is fuppreffed : here are alfo laid down the properties of 
elliptical and hyperbolical lenfes, with the pradtice of 
grinding glades. Dr. Barrow has treated on dioptrics in 
a very elegant manner, in his Optical Lectures, read at 
Cambridge. There are alfo Huygen’s Dioptrics, an ex¬ 
cellent work of its kind. But this part of optics was not 
perfedted till the difcovery of Dollond’s acromatic glafles, 
by which the colours are obviated in refradtingtelefcopes. 
The laws of refradtion of the rays of light in mediums 
differently terminated, that is, whofe furfaces are plane, 
concave, and convex, make the fubjedt of dioptrics. By 
refraction it is, that convex glafles, or lenfes, colledt the 
rays of light, magnify objedts, burn, See. and hence the 
invention of all kinds of dioptrical inftruments and ma¬ 
chines, from Ample fpedtacles to the molt improved mi- 
crofcopes, telefcopes, &c. The properties of the camera 
obfeura, magic lantern, and other fimilar illufions, are 
referrable to the fame law's; which fee under all thofe 
refpedtive articles, and particularly under Optics. 
DIORRHO'SIS, [from and 0^05, the ferum.] A 
converfion of the humours of the body into ferum and 
wafer. 
DIORTHO'SIS, f. [^lOfSwvir, of ^K>g 9 v&;, Gr. to make 
ftraight.] A chirurgical operation, by which crooked or 
difforted members are reffored to their primitive and re¬ 
gular fliape. 
DI'OS GYS, a town of Hungary: thirty-two miles 
weft of Tokay. 
DIOSCO'R.EA, f. [fo named in honour of Pedacivs 
Diofcorides, author of the Materia Medica in Greek.] In¬ 
dian Yam : in botany, a genus of the clafs dioecia, or¬ 
der hexandria, natural order farmentaceae, (afparagi, 
JuJf.) The generic charadlers are—I. Male. Calyx : 
perianthium one-leafed, bell-form, fix-parted; divifions 
lanceolate, fpreading at the top. Corolla: none; un- 
lefs you take the calyx for it. Stamina : filaments fix, 
capillary, very Ihort; antherae fimple. II. Female. Ca¬ 
lyx : perianthium as in the male. Corolla: none. Pif- 
tillum : germ very fmall, three-fided ; ftyles three, fim¬ 
ple ; ftigmas fimple. Pericarpium: capfule large, trian¬ 
gular, 
