At the same time, he was equally certain that life must have had an inorganic origin and that Science bids us so to believe. His various utterances are not, it is true, very easily reconciled. On the one hand he lays it down that "Without verification a theoretic conception is a mere figment of the intellect." On the other hand in his Belfast Address he thus expressed himself: Believing, as I do, in the continuity of nature, I cannot stop abruptly where our microscopes cease to be of use. Here the vision of the mind authoritatively supplements the vision of the eye. By a necessity engendered and justified by Science I cross the boundary of the experimental evidence.... If you ask me whether there exists the least evidence to prove that any form of life can be developed out of matter, without demonstrable antecedent life.... [men of science] will frankly admit their inability to point to any satisfactory experimental proof that life can be developed, save from demonstrable antecedent life. Far, however, from being a mere figment, his mental vision is represented as the most unalloyed product of reason. He writes:[85] Were not man's origin implicated, we should accept without a murmur the derivation of animal and vegetable life from what we call inorganic nature. The conclusion of pure intellect points this way and no other. The conclusion of pure intellect, however, having nothing to show for itself in the way of evidence, we are again referred to a condition of things concerning which we know, and can know, nothing. Supposing [writes the Professor][86] a planet carved from the sun, set spinning round an axis, and revolving round the sun at a distance from him equal to that of our earth, would one of the consequences of its refrigeration be the development of organic forms? I lean to the affirmative. It is no doubt interesting to know to what opinion the Professor inclined, but is this sort of thing Science? In the same manner Mr. Herbert Spencer, the philosopher of evolution _par excellence_, thus reports:[87] Biologists in general agree that in the present state of the world no such thing happens as the rise of a living creature out of non-living matter. They do not deny, however, that at a remote period in the past, when the temperature of the surface of the earth was much higher than at present, and other physical conditions were _unlike those we know_,[88] inorganic matter, through successive complications, gave origin to organic matter.[89]