[Sidenote: Its ancient decline.] A vast body of evidence has, however, come into prominence, establishing with equal certainty that there was in ancient times a far higher temperature in the planet; not a temperature concerned with a fraction of a degree, but ranging beyond the limits of our thermometric scale. The mathematical figure of the earth offers a resistless argument for its ancient liquefied condition--that is, for its originally high temperature. But how is this to be co-ordinated with the conclusion just mentioned? Simply by the admission that there have elapsed prodigious, it might almost be said limitless, periods. [Sidenote: Necessity for a long time.] As thus the true state of affairs began to take on shape, it was perceived that the age of the earth is not a question of authority, not a question of tradition, but a mathematical problem sharply defined: to determine the time of cooling of a globe of known diameter and of given conductibility by radiation in a vacuum. In such a state of things, what could be more unwise than to attempt to force opinion by the exercise of authority? How unspeakably mischievous had proved to be a like course as respects the globular form of the earth, which did not long remain a mere mathematical abstraction, but was abruptly brought to a practical issue by the voyage of Magellan's ship. And on this question of the age of the earth it would have been equally unwise to become entangled with or committed to the errors of patristicism--errors arising from well-meant moral considerations, but which can never exert any influence on the solution of a scientific problem.