(172 OPT 
in thofe fquares which correfpond with the divifions upon 
the rulers. For the breadth of objects, move the perpen¬ 
dicular ruler fo as to be even with the Tides of an objedf; 
and the divifions upon the lower ruler will (how their 
apparent breadths. After the fame manner, get the 
places and apparent fizes of as many principal objedts, 
as are neceffary for affifting you in completing the whole 
drawing, which may be done by this method with great 
ICS. 
exadlnefs. When the drawing is finifhed, the inftrument 
may be taken to pieces and put into a box, which may 
ferve as a drawing-board ; the top, fig. 10, may be ferew- 
ed into the (faff, which will ferve as a walking-ftick, and 
the (tool to fit on may be made very portable : fo that 
every part of this apparatus may be carried by one perfon 
without any inconvenience. Kirby, b. ii. 
INDEX to the Article OPTICS. 
A BERRATION from the unequal refran- 
gibiiity of the rays of light, 658 ; from 
the fpherical form of refledting and re¬ 
fracting furfaces, 661. 
Adams (Dudley), patent for rendering tele- 
fcopes portable, 605. 
Adams (Mr.) his improvement of Culpeper’s 
microfcope, 617, 18. 
Adams, jun his lucernal microfcope, 621, 2; 
his needle micrometer, 630. 
Aguilonius of Brufi'els, 546. 
D’Alembert, his propofals for improving 
achromatic telefcopes, 550. 
Alhazen, the great Arabian aftronomer, 542; 
his ideas as to refradtion, 547, 8. 
Anamorphofis, or re-formation of diftorted 
images, 668, 9. 
Antonio de Dominis, archbifhop of Spalatro, 
explains the phenomena of the rainbow, 
544. 594- 
Archimedes’s burning-glaffes, 544. 
Ariftotle, his ideas of the phenomena of light 
&c. 541, 552; defended by Du Hamel, 
545- 
Atmolphere, refradtion of, not uniform, 
551 ; how accounted for by Euler, &c. 
5.S 2 - 
Bacon, Roger, gave bints which led to the 
invention of fpedtacles, 543 5 held fome 
abfurd notions, 548. 
Balter, his remarks on very-fmall globules 
for microfcopes, 613; his improvement of 
Wilfen’s microfcope, 614, 15. 
Barker’s refledting microfcope, 612. 
Barrow’s lediures on optics, 546 ; his theory 
of vifion, 585. 
Berkeley’s theory of vifron, 564. 
Biot, his experiment on the polarifation of 
light, 560; repeated by Dr. Brewfter, 
639, 40. 
Blair (Dr. Robt.) his curious difeoveries on 
the fubjedt of refradtion, 55J. 
Blair (Mr. Robt.) 605. 
Bofcovich, his achromatic eye-piece for 
telefcopes, 603. 
Bouguer, his enquiries concerning the re¬ 
flection of light, 552, 5 5 his photometers 
for meafuring the inteniity of light, 632. 
Boyle, Hon. Robert, experiments of, 547, 
8 on the reflecting powers of light and 
dark bodies, 552. 
Bradley’s inftrument diftinguiflied from the 
kaleidofcope, 651, 2. 
Breguet’s micrometer, 657. 
Brereton, lord, notices a difference between 
glafs from a north and a fouth window, 
55 n , ■ . 
Btewfter, hrs numerous and currous experi¬ 
ments on the polarifation of light, 559, 
which led to the invention of the kalei¬ 
dofcope, 630; his fixed-wire and mother- 
of-pearl microfeopes, 629; his kaleido- 
fcopes fully deferibed, 638-52. 
Brown’s horizontal refledting telefcope, 605. 
Butterfield’s method of making globules for 
microfeopes, 612, 13. 
Camera obfeura, invention of, 543 ; (fee vol. 
iii. p. 653.) improved by Dr. Brewfter, 
and by the Rev. Mr. Thomfon, 599 ; com¬ 
bined with a microfcope, 621. 
Cafiegrain’s refledting telefcope, 601 ; pro¬ 
perties of, 656. 
Catoptrics, cultivated before dioptrics, 541. 
Cavallieri’s difeovery in optics, 600. 
Cavallo's mother-of-pearl micrometer, 629, 
631. 
Cauftics, 596, 8. 
Clairaut, his experiments on the refradtion 
of light, 550 ; his explanation of the cur¬ 
vature of lenfes, ibid. 
Clichtovceus, his conjedture upon the double 
rainbow, 594. 
Colours difeovered by Grimaldi to proceed 
from refradtion, 549 ; fome perfons not 
able to diflinguifh, 590 ; others pretend 
to know by the touch, 591 ; ancient and 
modern theories, ibid ; new theory by 
Jofeph Reader, 591, 2 ; Morichini’s dif¬ 
eovery, 592. 
Coventry’s micrometers, 531. 
Culpeper’s microfcope, 617. 
Des Cartes aferibes the invention of the te¬ 
lefcope to Metius, 544 ; his conduct with 
regard to Snellius, examined, 545 ; his ex¬ 
planation of the law of refradtion, 548 ; of 
vifion, 564. 
Defchales, his experiments on the inflection 
of light, 556. 
Di Torre’s exceeding fmall globules for mi¬ 
crofeopes, 613. 
Divini’s microfcope, 611. 
Dollond, John, his curious experiments on 
the refradtive powers of different kinds 
of glafs, 549, 50 ; improvements on the 
telefcope by additional eye-glalfes, 602, 3. 
Dollond, Peter, his achromatic telefcopes, 
603, 4- 
Drebbel, the fuppofed inventor of the micro¬ 
fcope, and of the thermometer, 611. 
Du Hamel, a writer on optics, 545. 
Edwards, Rev. John, his refledting tele¬ 
fcopes, 602; his mode of forming the 
fpecula, 605. 
Ellis’s aquatic microfcope, 615. 
Epicurus, his theory of vifion, 541. 
Euclid, his treatife on optics, 541 , fome 
doubtful or erroneous pofitions of his, 
54 h 2 ; 
Euler, his experiments on refradtion, 549 , 
does juftice to Mr. Dollor.d’s merit and 
difeoveries, 550, I 3 his theory of atmo- 
fpherical refradtion, 552; his microfcope 
with fix glades, 612. 
Eye, form and humours of, 581; pheno¬ 
mena of vifion, 582; to fuit glades to 
fhorc and long fight, 583 ; fingle vifion 
with both eyes, 564, 584 ; deceptions in 
vifion, 584, 590; fome eyes unable to 
diftinguifh colours, 590, 1. 
Fergufon’s rule for putting a circle in per- 
fpedtive, 667. 
Fletcher of Breflaw, 549. 
Fontana, one of the claimants to the inven¬ 
tion of the telefcope, 600 ; and of the 
microfcope, 611. 
Galileo, not the inventor of the telefcope, 
545 j his firft inftruments, 600 ; proper¬ 
ties of his telefcope, 655. 
Gafcoigne, Mr. gave the firft hint of ami- 
crometer, 624. 
Gaflendi, a writer on optics, 545. 
Glafs for achromatic telefcopes, 550, 
Gray, Stephen, his lenfes for microfoopes, 
6r3. 
Gregory, the inventor of the reflecting te¬ 
lefcope, 546, 601 ; its properties, 656. 
Grey’s water-microfcope, 612, 615. 
Grimaldi’s difeoveries as to the inflexion of 
light, 546, 555; and the caufe of co¬ 
lours, 549. 
Hadley’s quadrant, properties of, 652, 3. 
Hamilton’s Stereography, 663, 664. 
Haukfbee’s inftrument for meafuring refrac¬ 
tion, 548. 
Heliodorus of Farida, 542. 
Herfchel’s telefcope, 601 ; conftrudtion of 
fully deferibed, 6c8, 9 ; he points out the 
imperfedtions of micrometers, 627 5 his 
lamp-micrometec, 628. 
Hooke, Dr. firft obferved the colours in 
thin plates of Mufcovy glafs, or talc, 5523 
his experiments on the inflexion of light, 
555 ; his glafs globules for microfcooes, 
613. 
Huygens, a writer and worker in optics, 
546, his theory of dioptrics examined, 
557' > improves the refradting teie- 
fcope, 600; his micrometer, 624. 
Janfen, the inventor of the telefcope and 
microfcope, 61 r. 
Inflection or diftradtion of light firft no¬ 
ticed by Grimaldi, a Jefuit, 546 ; his ex¬ 
periments and thofe of Dr. Hooke, 555 ; 
of Dechales and Newton, 556, 7. 
Inftruments ufed in the elucidation of this 
feience, 597 ; propofidons arifing from the 
properties of, 652 ; imperfections of, 658. 
Joblot’s microfeopes, 616. 
Jurin, Dr. his experimenrs on vifion, 566. 
Kaleidofcope, 638 5 firft invention of, 638 ; 
completed in its Ample form, 640 ; princi¬ 
ples of, 64 j ; effect of putting the objects 
or mirrors in motion, 643; polition of the 
eye, 645 ; conftrudtion of the Ample ka¬ 
leidofcope, 646 ; compound or telefcopic, 
648; polyangular, 649 ; microfcopic, 650; 
curious properties, 651 ; different from 
Bradley’s inllrument, 652. 
Kater, Capt. his argument in favour of 
Caflegrain’s telefcope, 601. 
Kepler, firft explained themechanifm of rhe 
eye, 544, 564 ; and the caufe of reflection, 
552 ; followed Galileo in improving the 
telefcope, 600. 
Kirby’s perfpedtive machine, 671,2, 
Kircher, his works on optics, 546. 
Klingenftierna, of Sweden, his experiments 
on refradtion, 549. 
Leeuvren- 
