"Good!" exclaimed Mr. Henderson, as he noted it. "The temperature is going down. I'd rather have it too cold than too hot. We can stand a minus fifty of cold better than two hundred and twelve of heat. We have fur garments with us." "It is still going down," remarked Jack, as he saw the red column drop down past the thirty mark. "Below freezing," added Mark. The spirits fell in the tube until they touched twenty-eight degrees, and there they remained. "Twenty-eight degrees," remarked Professor Henderson. "That isn't so bad. At least, we can stand that if we are warmly clad." "Yes, but it will be colder to-night," said Jack. For they had landed on the moon in bright sunlight. "To-night?" questioned the German scientist, with a smile. "Yes, it's always colder when the sun goes down," went on the lad. "You have forgotten one thing," said Mr. Henderson, with a smile at his young protégé. "You must remember, Jack, that the nights and days here are each fourteen days long--that is, fourteen of our days." "How's that?" asked Jack. "Why," broke in Mark, who was a trifle better student than was his chum, "don't you remember that the moon rotates on its axis once a month, or in about twenty-eight days, to be exact, and so half of that time is day and half night, just as on our earth, when it revolves on its axis in twenty-four hours, half the time is day and half the time is night." "Sure, I ought to have remembered," declared Jack. "Mark is right," added Mr. Henderson. "And, as we have most fortunately arrived on the moon at the beginning of the long day, we will have fourteen days of sunshine, during which we may expect the temperature to remain at about twenty-eight degrees. But now about the atmosphere." "We will test that directly," went on the German. "It will take some time longer, though." Various instruments were brought forth and thrust out of the opening in the side of the projectile, which opening was so arranged that it was closed hermetically while the instruments were put forth. Then the readings of the dials or scales were taken, and computations made. In fact, some of what corresponded to the moon's atmosphere was secured in a hollow steel cup and brought inside the _Annihilator_ for analysis. "Well," remarked Professor Roumann, as he bent over a test tube, the contents of which he had put through several processes, "I am afraid we cannot breathe on the moon." "Can't breathe on it?" gasped Jack. "Then we can't go out and walk around it." "I didn't say that," resumed the German, with a smile. "I said we couldn't breathe the moon's atmosphere. In fact there is nothing there that we would call atmosphere. There is absolutely no oxygen, and there are a number of poisonous gases that would instantly cause death if inhaled." "Then how are we to get out and hunt for those diamonds, Professor?" went on Jack. "Gee whiz! if I'd known that, I wouldn't have come. This is tough luck!"