"Mecanique Celeste" to unravel the mysteries of the heavens. It will
hardly be disputed that the book which he has produced is one of the
most difficult books to understand that has ever been written. In
great part, of course, this difficulty arises from the very nature of
the subject, and is so far unavoidable. No one need attempt to read
the "Mecanique Celeste" who has not been naturally endowed with
considerable mathematical aptitude which he has cultivated by years
of assiduous study. The critic will also note that there are grave
defects in Laplace's method of treatment. The style is often
extremely obscure, and the author frequently leaves great gaps in his
argument, to the sad discomfiture of his reader. Nor does it mend
matters to say, as Laplace often does say, that it is "easy to see"
how one step follows from another. Such inferences often present
great difficulties even to excellent mathematicians. Tradition
indeed tells us that when Laplace had occasion to refer to his own
book, it sometimes happened that an argument which he had dismissed
with his usual formula, "Il est facile a voir," cost the illustrious
author himself an hour or two of hard thinking before he could
recover the train of reasoning which had been omitted. But there are
certain parts of this great work which have always received the
enthusiastic admiration of mathematicians. Laplace has, in fact,
created whole tracts of science, some of which have been subsequently
developed with much advantage in the prosecution of the study of
Nature.

Judged by a modern code the gravest defect of Laplace's great work is
rather of a moral than of a mathematical nature. Lagrange and he
advanced together in their study of the mechanics of the heavens, at
one time perhaps along parallel lines, while at other times they
pursued the same problem by almost identical methods. Sometimes the