"It could hardly have been the direct action of the sunlight," he replied. "It must have resulted from some accidental concentration of the solar rays upon an inflammable substance by a mirror." "I recall seeing a large concave glass on the principal platform in which they were fond of looking at their magnified images," I said. "Yes, and no doubt that was the instrument chosen by fate to bring about this terrible end. The power of the sunbeams is twice as great here as upon the earth, and the heat in the focus of a mirror a couple of feet in diameter would suffice to set fire to the flimsy materials which abounded on the tower. Once started in such a place it ran like sparks in a train of gunpowder." "But the madness that seized the multitude before the catastrophe--what did you mean by saying that it was the ultraviolet rays?" "I used the term," Edmund replied slowly, "without attaching a very clear meaning to it. It simply expressed the general thought that was in my mind. It may be some other form of solar radiation to which we are not accustomed on the earth, but which is specially effective here when the sun is uncovered because of the greater nearness of Venus. This atmosphere, notwithstanding its density, may well be diaphanous to the ultraviolet rays, owing to some peculiarity in its composition which I have not had time to study. At any rate, it is evident, from what we have seen, that the rays of the unclouded sun almost instantly affect the brain. I, myself, felt them as if a thousand needles had been thrust through my skull; and I believe that they are responsible, rather than the shock of the wound in my side, for my present weakness." "And did you foresee the consequences of the uncovering of the sun?" "Not altogether. I had been led to think that something extraordinary must accompany the periodical appearances of the great orb, and if I could have known that an apparition was at hand I might have made preparations for it and we might have been able to save Ala. When I saw what was going on, I tried to reach her, and you know the result." "But is it not incredible that a people of so peaceable a disposition should be seized with such murderous instincts when driven out of their senses by the effect of the rays?" "No, it does not seem so to me. You know the general tendency of sudden madness, which usually produces a complete reversal of the ordinary instincts of the demented persons, making them dangerous to their dearest friends. But why talk longer of this? It is too painful--too overwhelming. What can man do against the great forces of Nature? At this moment I solemnly declare to you that I regret that I ever entered upon this expedition."