11 E T 



It E T 



farther on, wooded mountains : — to tlie welt, the citadel, 

 the harbour, and the fea. In a word, every thing concurs 

 to render Retimo the moft agreeable town in the ifland. 

 It would alfo have become, perhaps, the richeft, and the mod 

 populous, if the harbour, fmall as it is, had been kept in 

 order. At prefent it is only practicable for the barks of 

 the country ; (hips remain in the road, but rarely anchor 

 here ; and thus Retimo, which, from its pofition, the abun- 

 dance of oil which is collected in its vicinity, and the other 

 productions of its territory, might be an important place of 

 trade, has, as well as Candia, feen a part of its population 

 pafs to Canea. Its prefent population, fays Olivier, con- 

 fills of from 5 to 6000 inhabitants, half Greeks, halt Turks : 

 the Jew- here are not fo numerous as at Candia. 



This town, weakly defended, was plundered and ravaged 

 by the Turks, as far back as the year 1572, while Selim II. 

 was caufing the fiege of Famagufta, in Cyprus, to be 

 pulhed on with vigour j but it was not till the reign of 

 Ibrahim,"in 1645, that the Venetians were driven from it 

 for ever; 40 miles W. of C. idia'. N. lat. 35 20'. E. 

 long. 24 21'. 



The province of Retimo is one of the beft cultivated 

 and moll productive of the ifland ; it furnilhes a great deal 

 of oil, a little bariey ami wheat, and a tolerably large 

 quantity of wine. The riling grounds and hills which 

 lkirt the fliores of Armiro are almoil all covered with vines. 

 On the ncarell mountains which lie to the fouth, is a foreft 

 of common and native oaks, maples, and carob-trecs, into 

 which the inhabitants of Retimo come to cut the wood, of 

 which they Hand in need. To the fouth of Retimo are the 

 two provinces of Ai'on-Vail'ali and Amuri, the only ones that 

 are comprifed in this pachalic ; they furnifh wheat, barley, 

 oil, and fome fruits. The former, iituated to the N.W. of 

 the other, furnilhes, belides, excellent cheefe, which is con- 

 founded in trade with that of Sphachia. The Greeks are 

 more numerous than the Turks in the provinces of Ai'on- 

 Vafl'ali and Amuri. Olivier and Sonnini. 



RETINA, m. Anatomy, a membrane of the eye, formed 

 by the expanfion of the optic nerve, and conitituting the 

 immediate organ of vilion. See Eye. 



RETINA, in Optics. The retina is ufualiy fuppofed to 

 be the great organ of vifion, which is ellected by means of 

 the rays of light reflected from each point of the objects 

 refracted in their pafiage ti. he aqueous, vitreous, 



and cryltalline humours, and tl rown on the retina, 



where they paint the image of the object ; and where they 

 make an impreflion, which is continued thence, by the fine 

 capillaries of the optic nerves, to the fenfory. Sec Eyu 

 and Vision. 



Indeed, whether the retina, or the choroides, be tin- 

 principal organ of vilion, and that on which the in 

 of objects are reprefented, has been much controverted be- 

 11 Ieveral members of the Royal Acad .m> ; particularly 

 Ah ilr . Mariotte, Pecquet, Perrault, Mery, and de la Hire. 

 Mariotte lirll referred rifion to the choroides, and was 

 feconded by Mery ; the relt aflerted the caufe of the 

 retina. 



'I'll ■ retina was always ju all the chara&ers 



of tin- principal organ. It is utuated in the focus of th 

 fraction of the humour-, ol the eye; and • ' '-nee 



receives the vertices of the cones of raj , proc edinj 

 thr Ieveral points of objects. It is very thin, and 

 fequentli Gble. It has its origin from the 1 



Li holly nervous j and i 



opinion, 'hat the nerves are the vehicli 1 II nfatione. 

 JLallly, 1! nicates with the fubllancc of the brain, 



where all fenfatious terminate. 



As to the choroides, its ufe was fuppofed to be to flop 

 the rays, which the extreme tenuity of the retina fhould 

 let pals ; and to do the fame office with refpeft to the re- 

 tina, which the quickfilver does to a looking-glafs ; efpe- 

 ciaHy in thofe animals in which it is black. 



But from an experiment of a cat plunged into water, 

 M. Mery conceived a different opinion. (See Plpil.) 

 He obferved the retina to difappear abfolutely on that oc- 

 cafion, as well as all the other humours of the eye ; while 

 the choroides (till appeared dillinctly, and even with all the 

 lively colours which it has in that animal. Hence, he con- 

 cluded, that the retina was as tranfparent as the humours, 

 but the choroides opaque ; confequently the retina was 

 not a proper initrument to terminate and flop the cones of 

 •ays, or to receive the images of objects ; but that the 

 light mull pafs through it, and could only be flopped on 

 the choroides; which therefore would become the principal 

 organ of vifion. The black colour of the choroides in 

 man is extremely favourable to this opinion ; the principal 

 organ (liould feem to require, that the action of the light 

 fhould terminate on it as it arrives ; which it is certain it 

 here doi s in the black, that abforbs all the rays, and re- 

 flects none ; and it fhould alfo feem necellary, that the 

 action of the light fhould be flronger on the organ of fight 

 than any where elfe : now it is certain that the light, be- 

 ing received and abforbed in a black body, mull excite a 

 greater vibration there than any where elfe ; and hence it is 

 that black bodies are kindled by a burning-glafs much 

 {boner than white ones. 



The fituation of the choroides behind the retina is an- 

 other circumltance on its fide ; M. Mery having obferved 

 the fame pofition of the principal organ behind a mediate 

 organ in the other fenfes, which makes an happy analogy. 

 Thus the cuticle extended over the lkin is the mean organ 

 of feeling ; but the cutis underneath is the principal organ. 

 The like is obferved in the ear, nofe, eke. 



The retina, therefore, fhould feem a kind of mediate or 

 fecondary organ, ferving to break the too (Irong impref- 

 lion of the light on the choroides, or to preferve it ; which 

 is the ufe afcribed to the cuticle. Add to all this, that the 

 retina is iufenfible, as having its origin from the medullary 

 fubflance of the brain, which is fo too ; and the choroides, 

 on the contrary, is very fenfible, as arifmg from the pia 

 mater, which is certainly fenfible in a great degree. 



This laft argument being doubted of, M. Mery was en- 

 gaged to prove it; which he did before the Royal Academy, 

 where he fhewed that the optic nerve is not compofed, 

 like the other nerves, of fibres; that it is only a train of 

 the medulla inclofed in a canal, out of which it is ealily 

 fep arable. 



This ftrufture of the optic nerve, hitherto unknown, 

 MTS that the retina can be no membrane; it is only a 

 dilatation of the medulla, inclofed under two membra. 



and .1 pith or medulla C 0] t fubltance to be the 



in. It can fcara ly H rve tor any thing but to 

 filtrate the fpirits neceffary for the tioi vifion. The 

 ition, by which the fenfation il ■■ niull be 



1 1 1 a part more folid, more firm, and fufceptible 



of a li . in 1 flion. 



Fo 1 her arguments in favour of the choroides being 

 the feat ol vifioi 



R ETINACUL1 ' of a cl irurgical inftru- 



ment ufed in caftrati ition for a hernia* to 



,1 into the fcrotum. 



RETINARIA, in Botany, was fo called by Gartner, 



from relt, a net, or rather more immediately perhaps from 



I he 



