VOL. LXXXlII.j PHILOSOPHICAL TRANSACTIONS. 323 



dried preparations, he has imagined that each coat consists of circumvolutions 

 of a single fibre, and has entirely overlooked the attachment of the fibres to 

 tendons; and if the fibres were continued into each other in the manner that he 

 describes, the strict analogy to muscle would be lost, and their contraction could 

 not have that effect on the figure of the lens, which is produced by help of the 

 tendons. Yet notwithstanding that neither he, nor any other physiologist, has 

 attempted to explain the accommodation of the eye to different distances by 

 means of these fibres, still much anatomical merit must be allowed to the faith- 

 ful description, and elegant delineation, of the crystallines of various animals, 

 which he has given in the Phil. Trans, vol. 14, p. 780, and vol. 24, p. 1723. It 

 appears, from his descriptions and figures, that the crystalline of hogs, dogs, 

 and cats, resembles what I have observed in oxen, sheep, and horses; that in 

 hares and rabbits, the tendons on each side are only 2, meeting in a straight 

 line in the axis; and that in whales they are 5, radiated in the same manner 

 as where there are 3. It is evident that this variety will make no material differ- 

 ence in the action of the muscle. I have not yet had an opportunity of exa- 

 mining the human crystalline, but from its readily dividing into 3 parts, we may 

 infer that it is similar to that of the ox. The crystalline in fishes being spherical, 

 such a change as I attribute to the lens in quadrupeds cannot take place in that 

 class of animals. 



It has been observed that the central part of the crystalline becomes rigid by 

 age, and this is sufficient to account for presbyopia, without any diminution of 

 the humours; though I do not deny the existence of this diminution, as a con- 

 comitant circumstance. 



I shall here attempt the solution of some optical queries, which have not been 

 much considered by authors. 1 . Musschenbroek asks, what is the cause of the 

 lateral radiations which seem to adhere to a candle viewed with winking eyes? I 

 answer, the most conspicuous radiations are those which, diverging from below, 

 form, each with a vertical line, an angle of about 7"; this angle is equal to that 

 which the edges of the eye-lids when closed make with a horizontal line; and 

 the radiations are evidently caused by the reflection of light from those flattened 

 edges. The lateral radiations are produced by the light reflected from the edges 

 of the lateral parts of the pupillary margin of the uvea, while its superior and 

 inferior portions are covered by the eye-lids. The whole uvea being hidden before 

 the total close of the eye-lids, these horizontal radiations vanish before the per- 

 pendicular ones. 



2. Some have inquired, whence arises that luminovis cross, which seems to 

 proceed from the image of a candle in a looking glass? this is produced by the 

 direction of the friction by which the glass is polished: the scratches placed in a 



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