The most profound among the many eminent thinkers France has produced,
is Réné Descartes, of whom the least that can be said is, that he
effected a revolution more decisive than has ever been brought about
by any other single mind; that he was the first who successfully
applied algebra to geometry; that he pointed out the important law of
the sines; that in an age in which optical instruments were extremely
imperfect, he discovered the changes to which light is subjected in
the eye by the crystalline lens; that he directed attention to the
consequences resulting from the weight of the atmosphere; and that he
moreover detected the causes of the rainbow. At the same time, and
as if to combine the most varied forms of excellence, he is not only
allowed to be the first geometrician of the age, but by the clearness
and admirable precision of his style, he became one of the founders
of French prose. And, although he was constantly engaged in those
lofty inquiries into the nature of the human mind, which can never
be studied without wonder, he combined with them a long course of
laborious experiment upon the animal frame, which raised him to the
highest rank among the anatomists of his time. The great discovery
made by Harvey of the Circulation of the Blood was neglected by most
of his contemporaries; but it was at once recognised by Descartes, who
made it the basis of the physiological part of his work on man. He was
likewise the discoverer of the lacteals by Aselli, which, like every
great truth yet laid before the world, was at its first appearance,
not only disbelieved, but covered with ridicule.--_Buckle’s History of
Civilization_, vol. i.