In the previous portion of this paper, which appeared in the January Number, I examined the form in which Croll presented the astronomical theory of the Ice Age and endeavoured to show how absolutely unsound his argument is. It is, however, at least as necessary to discuss the form in which Sir Robert Ball presents it; for much of the recent success of the theory, outside the school of modern geologists, was due to the weight naturally attached to the fact that a writer of Ball's scientific eminence believed he had so materially strengthened Croll's astronomical argument, that had Croll himself been aware of its full force, he would not have felt bound to call in such auxiliary agencies as a diversion of the Gulf Stream from its course. If, then, the theory, as presented by Croll, was able to win its way with such success among scientific authorities, it must surely be irresistible in the new and more powerful form. But it will be seen that, so far from strengthening Croll's position, Ball's statement weakens it very materially.