542 PHILOSOPHICAL TRANSACTIONS. [aNNO 1681-2. 



upper, lower, or lateral parts of the thalami optici, confirm what has been 

 said. For the optic nerve consists of two coats, the exterior, being produced 

 from the dura mater, makes the sclerotica, as the interior, arising from the 

 pia mater, produces the uvea, and consists of medullary fibres, which being in a 

 distinct order expanded at their insertion into the bottom of the eye, form the 

 tunica retiformis. This coat looks at first view indeed like a mucous substance; 

 but if it be put into a crystal glass filled with clear water, and exposed to the 

 light or sun, after the other coats are removed, this coat will be very well ex- 

 panded (especially if the water be a little warm,) and will show all the fibrillse 

 very fairly and distinctly, like the fine threads of lawn, so that all these fibres 

 keep their due position, and answer to distinct parts of objects, and observe 

 that order or parallelism requisite to distinct vision. 



From what has been said, several problems concerning vision may be 

 solved. As, 



1. Why vision is not double, since the organ is so ? The answer is, because 

 the fibrae Concordes are like unisons in a lute, and the rays strike both at the 

 same time. 



2. Hence also it appears, why upon pressing down one eye, an object appears 

 double ? viz. because thereby its rays fall upon discordant fibres in the other 

 eye not pressed, so that there are two different sensations. 



^n explanation of the Figure 4, pi. 15. — a a, bb, cc, dd, &c. are the fibras 

 Concordes of the optic nerves, as they arise alike from the thalami optici ////, 

 which run also to like parts of the eye; where note that a a are the two upper- 

 most fibres, and are supposed to have the greatest flexure ; bb, cc, dd, the ex- 

 ternal-lateral fibres; ee,ff, gg, the internal-lateral; ////, the two protuberances, 

 called thalami nervorum opticorum, from whence the optic nerves have their 

 rise ; hhhhh, the parts of the brain that lie under them ; ii, the optic nerves, 

 made here the larger to express as many of their fibres as could be distinctly re- 

 presented; +, the place of their union; mm, the eyes divested of the sclerotica 

 and uvea; nn, the processus ciliares lying just under the iris; oo, the pupils or 

 sights. ■ 



A short Relation out of the Journal of Capt. Abel Jansen Tasman, on the Dis- 

 covery of the South Terra Incognita; 7iot long since published in the Loiu Dutch. 

 By Dirk Rembrantse. Philos. Collect. N° 6, p. 1 79. 



The geographical accounts given by this celebrated Dutch navigator, are super- 

 seded by the more exact observations and discoveries of our own countryman. 

 Captain Cook. 



