VOL. XXXIII.] FHILOSOPHICAL TRANSACTIONS. 71 



by the 5 true ribs. They were pretty thick, about the middle, and exceedingly 

 thin and sharp towards the extremities. 



The eye externally, somewhat resembled the human eye, except that it was 

 less convex, with a free and moveable upper eye-lid, with eye-lashes, as most 

 terrestrial animals have, besides a tunica nictitans, as in other birds. Besides 

 the 7 muscles of the eye, as they are in brutes, it had 2 more, one arising from 

 the forepart of the sclerotica, which soon formed a small tendon, obliquely 

 surrounding the optic nerve, and then joined to another muscle, which arises 

 opposite to the former, from which the tendon continues its way, and is inserted 

 in the tunica nictitans. The aqueous humour was in greater quantity than com- 

 mon. • The crystalline was of an uniform substance, but less convex on the in- 

 side, than without. The vitreous was small in quantity, considering the size 

 of the eye ; the choroides was entirely black, without that variety of colours at 

 its bottom, which is common to most brutes. The fore part of the sclerotica, 

 where it is annexed to the cornea, was bony, consisting of 15 bony scales joined 

 to one another, so as to make one circular bone round the cornea. 



As for a more particular description, I refer to the anatomical account given 

 by the Royal Academy at Paris, in their Natural History of Animals, and to 

 Vallisneri, professor at Padua, in his Notomia del Struthio. 



An Account of the Appearance of Mercury, passing over the Sims Disk, 

 Oct. 'ig, 1723; determining the mean Motion, and fixing the Nodes of that 

 Planet's Orbit. By Dr. Edmund Halley. N" 386, p. 228. 



The transit of the planet Mercury, over the sun's disk, being one of the 

 most curious and uncommon appearances that the heavens afford, astronomers, 

 both at home and abroad, made due preparation to observe, with the utmost 

 exactness, that which happened on the 29th of October, 1723, which the 

 Doctor had predicted in the year 1691 (Phil. Trans. N" ip3) would be in part 

 visible in England. And the sky proving very favourable at that time, the in- 

 gress on the sun's limb was observed with the greatest accuracy. 



Accordingly, the same day, Oct. 29, O. S. at Greenwich, in the Royal 

 Observatory, the Doctor first perceived, with the 24-foot tube, the planet 

 making a small notch in the sun's limb, at 2*^ 41™ 23^ apparent time. And at 

 2^ 42*" 26^ he was wholly entered, making an interior contact, the light of the 

 sun's limb just beginning to appear behind his dark body ; which, notwith- 

 standing the slowness of the motion, was in a manner instantaneous. Then, 

 applying the micrometer to the said 24-foot tube. Dr. H. opened it so as to 

 take in 16' 15", equal to the sun's semidiameter at that time ; and causing the 



