102
The specific gravities of the different parts are as follows, that of distilled water being 1:
| In the Ox. | In the Codfish. | |
| Aqueous humour | 1 | 1 |
| Vitreous humour | 1.016 | 1.013 |
| Christalline lens (mean) | 1.114 | 1.165 |
| Outer part of ditto | 1.070 | 1.140 |
| Inner | 1.160 | 1.200 |
As to their refracting powers, they must be more considerable than their density indicates, on account of the inflammable particles which enter into their composition. It is possible also, that the proportional quantity of these inflammable particles may not be the same in the different humours, so that their refracting powers may not be exactly in the ratio of their densities. (Cuvier.)
Dr. Wollaston makes the refracting power of the vitreous humour equal to that of water, and that of the chrystalline lens of the ox greater in the ratio of from 1.38 to 1.447 to 1. Dr. Brewster gives the following Table deduced from experiments made on a recent human eye:
| Refracting power of |  |
water | 1.3358 |
 |
the aqueous humour | 1.3366 | |
|
the vitreous humour | 1.3394 | |
 |
the outer coat of chrystalline | 1.3767 | |
|
the middle | 1.3786 | |
|
the central part | 1.3990 | |
 |
the whole chrystalline | 1.3839 |
Dr. Brewster gives also the following dimensions:
| Inch. | |
| Diameter of the chrystalline | 0.378 |
| Diameter of the cornea | 0.400 |
| Thickness of the chrystalline | 0.172 |
| Thickness of the cornea | 0.042 |
137. The construction of the eye being so far explained, we may now detail the circumstances attending vision, as far as we are acquainted with them.
