Had my spirit really been transported to the planet Mars, or had I been the dupe of a purely imaginary illusion? The feeling of reality had been so strong, so intense, and the things I had seen agreed so perfectly with the scientific notions which we already possess in regard to the physical nature of the Martial world, that I could not entertain a doubt on the subject, although amazed at that ecstatic trip, and asking myself a thousand questions, each one contradicting the other. Spero's absence in all that vision puzzled me a little. I still felt so closely attached to his dear memory that it seemed to me as if I should have been able to detect his presence, to fly directly to him, see him, speak to him, hear him. But was not the man hypnotized at Nancy the toy of his own imagination, or of mine, or of the experimenter's? On the other hand, even admitting that my two friends had been reincarnated upon that neighboring planet, I reflected that beings might easily not meet one another in going about the same city, and in a world the chances were infinitely less. And yet surely it was not the doctrine of chances which should be invoked in this case; for such a feeling of attraction as that which had united us ought to increase the probability of our meeting, and throw an element into the scale which should outweigh all the rest. [Illustration] Talking thus with myself, I went back to my observatory at Juvisy, where I had been preparing some electric batteries for an optical experiment with the tower of Montlhéry. When I had satisfied myself that everything was in readiness, I left the task of making the signals agreed upon, between ten and eleven o'clock, to my assistant, and went to the old tower, where I installed myself an hour later. The night had come. From the top of the old donjon the horizon is perfectly circular, entirely free in all its circumference, which extended on a radius of twenty to twenty-five kilometres all around this central point. A third post of observation, situated in Paris, was in communication with us. The object of the experiment was to find out whether the rays of different colors of the luminous spectrum all travel with the same speed,--300,000 kilometres a second. The result was affirmative. [Illustration] The experiments were ended at about eleven o'clock, the starry night was marvellous, and the moon was beginning to rise. As soon as I had put the apparatus under cover inside the tower, I went to the upper platform again, to look at the broad landscape lighted by the first rays of the waxing moon. The atmosphere was calm, mild, almost warm. But my foot was still on the last step when I stopped, terror-stricken, uttering a cry which seemed to die away in my throat. Spero, yes, Spero himself, was there, before me, seated on the parapet! I threw up my arms, and felt as if I were going to faint; but he said in his gentle voice, which I knew so well,-- "Do I frighten you?"