Mr. Home's Lecture 
Being unwilling that a subject on which Mr. Hunter had 
so publicly given his opinion should remain in an unfinished 
state, I requested the President's permission to be allowed to 
give the Croonian lecture for the present year, as it would 
afford me an opportunity of weighing with impartiality the 
facts already ascertained, and of endeavouring by my own la- 
bours to add to their number. 
In prosecuting this inquiry, I consider myself to have been 
particularly fortunate in having had the assistance of my friend 
Mr. Ramsden. It was a subject connected with his own pur- 
suits, and one which had always engaged his attention ; he 
was therefore peculiarly fitted, both by his own ingenuity 
and knowledge in optics, for such an investigation. 
In conversing upon the different uses of the crystalline hu- 
mour, he made the following observations. 
He said, that as the crystalline humour consists of a sub- 
stance of different densities, the central parts being the most 
compact, and from thence diminishing in density gradually in 
every direction, approaching the vitreous humour on one side, 
and the aqueous humour on the other, its refractive power be- 
comes nearly the same with that of the two contiguous sub- 
stances. That some philosophers have stated the use of the crys- 
talline humour to be, for accommodating the eye to see objects 
at different distances ; but the firmness of the central part, and 
the very small difference between its refractive power near the 
circumference and that of the vitreous, or the aqueous humour, 
seemed to render it unfit for that purpose ; its principal use 
rather appearing to be for correcting the aberration arising 
from the spherical figure of the cornea, where the principal 
part of the refraction takes place, producing the same effect 
