Convergence of Rays in the Aqueous Humor of the Eyeball
The convergence of light rays in the eyeball begins in the aqueous humor is perfected in the crystalline. But when they strike the vitreous humor, which is concave on its front surface, and also less dense than the crystalline, they diverse or spread out, and are thrown upon the back part of the eye.
Lee, Charles A. Human Physiology for the Use of Elementary Schools, 11th ed. (Buffalo: J. C. Derby & Co., 1847) 207