150 FORMATION OF SHELLS OF ANIMALS, ETC., 
(Indeed gravity is not a universal influence, if its operation 
isto be excluded from the process bywhich the lensof the eye 
is formed; and its laws are not those which mathematicians 
and philosophers have unanimously considered them, if a 
lens formed in complete obedience thereunto would not 
have been, in respect to vision, a useless one.) Hence the 
impossibility of anythimg short of itricacy in the 
mechanism of an organ constructed under circumstances 
where the principal force employed in the process is 
always working in the wrong direction, and is therefore 
requiring constantly to be opposed, and to be put imto the 
right track. Now these ends seem to be attained in the 
case of the crystalline lens, by its bemg composed of 
globules of such a composition that they do not coalesce 
until the more fluid part has been removed; and thus in 
place of being made up at once of all the molecules 
entering into the composition of the globules at first 
collected together, as in the artificial calculi, it is formed 
only by the gradual coalescence of their denser portions, 
and especially of their outer lamime. Besides these 
physical peculiarities, it has been observed that the 
coalescence is accompanied by a chemical change in the 
coalesced particles, as is shown by the fact of their 
retaining their transparency after bemg boiled in water, 
and by their density becoming increased as the coalescence 
progresses, and attains its ultimate condition of com- 
pleteness in the centre of the lens, an effect the opposite 
of that which would have been produced by the uncon- 
trolled action of gravity. Hence in the general arrange- 
ment of the particles composing the crystalline lens, the two 
attractions mentioned at pages 32 and 55—the attraction of 
tenacity,and the attraction of gravitation—musthave acted 
inversely as each other. But the latter being universal, 
