DIO 
ript. 
own, a ufual with him under fuch circumftancer, 
ific charaéter; the following is taken 
m novan’s {plendid illuftration of the infeéts of 
‘India, in which this extraordinary infe& is defcribed at con- 
fiderable length, with an appropriate accompaniment of 
fi 
capite abdomine antice 
— ‘Black; 
o 
head, anterior part of the abdomen and legs ferruginous: 
. 23 
p 
ct 
er 
oO 
nm 
4 
et 
bat} 
oO 
B 
> 
<j 
5 
a 
et 
x 
i=] 
extremity of elongated pedicles, as is for examp!e initanced in 
d 
direéted towards any obje&t at the will of the animal with 
but, to accomplith this, the motion of 
el y. The eyes of 
r are notwith{tanding fo conveniently ftationed at 
rality of infcts. 
“To the inexperienced entomologift, the dioplis would 
k 
e 
exadly known. Fuedly, notwithftanding, defcribes the latter 
nea, perhaps with as little reafon. Lia- 
treille tells us, it is from the coatt of Angola, on the iu:form- 
fpecimens were brought from Bengal; it was difcovered by 
Mr. Fichtel, who has thus eftablifhed the babitat of this 
fingular creature beyond difpute.”? Vide Jnf- India. 
This i is rather larger than the common houfe-fly, 
and is very fcarce. 
DIOPTER, or Dioptra, in Writers of Aftronomy, is fre- 
quently ufed for the hole, or index, pierced in the pinnula, 
or fight of analhidade. See Sicurs. 
DIO 
DIOPTRA, among the Ancients,an inftrument invented by 
‘Lipparchus, which ferved for feveral ufes, as to level water, 
10 
by to d d infpe& any ulcers 
therein ; called alfo {peculum matricis and dilatatorium. 
DIOPTRI O Greek Sion loprcct, to fee 
tics, and tre 
the different refraGions of light paffing through differeot 
mediums, fuch as g i —When the rays of 
direGion from one medium into 
othe ich is otherwife ftraight, is ge. 
nerally bent at t oint of tranfition, and that bending is 
called the refra@ion of light, the quantity of which differs in 
different mediums. 
In their tranfition from one medinm into another, the rays 
of light, befides their being bent or refra€ted, fuffer a fort 
The rain-bow, the colours of thin tran~ 
mena, arife from the refra€tion of light; the a€tion of the 
telefeopes and microfcopes that are conftru€ted with glafs 
lenfes, the aGiion of the camera obfcura, of {peQiacles, and 
or from the latter into the former, or, in genera 
tranfparent medium into another tranfparent fubftance of 
ifferent denfity, then they are refrade js 
rti if, in 
furfac medium, th:y fall perpendicularly upon it ; 
or if they continue in the fame medium, then they proceed 
in ftraight lines without any perceptible deviation one way 
ight of the ccleftial objeéts, in its paf- 
or another. eli 
{ 
ve : 
the air at different diftances from the furface of the earth. 
The refraction of light may be illuftrated by the following . 
eafy and familiar experiments. 
1. Provide a glafs veflel A BC, (Plate IV. Optics, jig. 2.)3 - 
lay a card, having a {mall hole F in its middle, upon the aper- 
ture of it, and fix a candle or lamp E above the veffel, fo that - 
its flame may ftand perpendicularly over the hole F in the card, 
which may be eafily accomplifhed by means of a plummet. 
In this fituation of the apparatus.the image of the hole will be 
caftat D, upon the bottom of the veflel; and the line which 
the light of t 
falling perpendicularly upon the furface re) 
proceeds in a ftraight line to D, without fuffering any bend- 
ing or refraction at the point of its entrance into the water. 
2..Take a veflkl ABDC, jig. 3. open at top, place 
a light 
