calculation by which Laplace thought he had provided an explanation
of this acceleration was erroneous. Adams, in fact, proved that the
planetary influence which Laplace had detected only possessed about
half the efficiency which the great French mathematician had
attributed to it. There were not wanting illustrious mathematicians
who came forward to defend the calculations of Laplace. They
computed the question anew and arrived at results practically
coincident with those he had given. On the other hand certain
distinguished mathematicians at home and abroad verified the results
of Adams. The issue was merely a mathematical one. It had only one
correct solution. Gradually it appeared that those who opposed Adams
presented a number of different solutions, all of them discordant
with his, and, usually, discordant with each other. Adams showed
distinctly where each of these investigators had fallen into error,
and at last it became universally admitted that the Cambridge
Professor had corrected Laplace in a very fundamental point of
astronomical theory.

Though it was desirable to have learned the truth, yet the breach
between observation and calculation which Laplace was believed to
have closed thus became reopened. Laplace's investigation, had it
been correct, would have exactly explained the observed facts. It
was, however, now shown that his solution was not correct, and that
the lunar acceleration, when strictly calculated as a consequence of
solar perturbations, only produced about half the effect which was
wanted to explain the ancient eclipses completely. It now seems
certain that there is no means of accounting for the lunar
acceleration as a direct consequence of the laws of gravitation, if
we suppose, as we have been in the habit of supposing, that the
members of the solar system concerned may be regarded as rigid