Kepler should have been so wasted, and it is difficult not to suspect at
times that some of the valuable results which lie embedded in this great
mass of tedious speculation were arrived at by a mere accident. On the
other hand it must not be forgotten that such accidents have a habit of
happening only to great men, and that if Kepler loved to give reins to
his imagination he was equally impressed with the necessity of
scrupulously comparing speculative results with observed facts, and of
surrendering without demur the most beloved of his fancies if it was
unable to stand this test. If Kepler had burnt three-quarters of what he
printed, we should in all probability have formed a higher opinion of
his intellectual grasp and sobriety of judgment, but we should have lost
to a great extent the impression of extraordinary enthusiasm and
industry, and of almost unequalled intellectual honesty which we now get
from a study of his works."

Professor Forbes is more enthusiastic. In his "History of Astronomy," he
refers to Kepler as "the man whose place, as is generally agreed, would
have been the most difficult to fill among all those who have
contributed to the advance of astronomical knowledge," and again _à
propos_ of Kepler's great book, "it must be obvious that he had at that
time some inkling of the meaning of his laws--universal gravitation.
From that moment the idea of universal gravitation was in the air, and
hints and guesses were thrown out by many; and in time the law of
gravitation would doubtless have been discovered, though probably not by
the work of one man, even if Newton had not lived. But, if Kepler had
not lived, who else could have discovered his Laws?"