"That is pure speculation," he explained. "And very easy speculation, too. Any one can allow his imagination to run wild and picture strange beings of another world. I don't predict they will actually land on the earth--and I have no idea what they will look like if they do land. As a matter of fact, they will probably look very much like ourselves. I see no reason to doubt it." "Like us?" I ejaculated. "Why not?" said Alan. "Conditions on Mercury are not fundamentally different from here. We don't have to conceive any very extraordinary sort of being to fill them." "Here's what you can tell your paper," said the professor abruptly. "Take it down." I took out my notebook, and he dictated briskly. "Regarding the possible characteristics of inhabitants of Mercury, it is my conception that intelligent life--let us say, human life--wherever it exists in our universe does not greatly differ in character from that of our own planet. Mars, Venus, Mercury, even Neptune, are relatively close. I believe the Creator has constructed all human life on the same general plan. "I believe that, being neighbors--if I may be permitted the expression--it is intended that intercourse between the planets should take place. That we have been isolated up to the present time is only because of our ignorance--our inability to bridge the gap. I believe that migration, friendship, commerce, even war, between the inhabitants of different planets of our solar system was intended by Almighty God--and, in good time, will come to pass. "This is not science; and yet science does not contradict it, in my opinion. Human life on Mercury, Venus or Mars may need bodies taller, shorter, heavier, lighter, more fragile or more solid than ours. The organs will differ from ours, perhaps, but not materially so. The senses will be the same. "In a word, I believe that nearly all the range of diversity of human life existing on any of the planets exists now on this earth, or has existed in the past, or will exist in the future through our own development, or at most the differences would not be greater than a descent into our animal kingdom would give us. "Mercutians may have the sense of smell developed to the point of a dog; the instinct of direction of the homing pigeon; the eyes of a cat in the dark, or an owl in the light; but I cannot conceive of them being so different that similar illustrations would not apply. "I believe the Creator intends intercourse of some kind, friendly or unfriendly, to take place between the worlds. As China was for centuries, so for eons we of this earth have been isolated. That time is past. The first act was one of aggression. Let us wait for the next calmly but soberly, with full realization of the danger. For we may be--indeed, I think we are--approaching the time of greatest peril that human life on this earth has ever had to face!" CHAPTER III. THE LANDING OF THE INVADERS.