stant presence of clouds which were down to a very low level although the horizon was clear, a condition that often prevails both in the Arctic and Antarctic Regions: this method allowed of a certain amount of exploration of the atmosphere though not so extensive as the method employed when the sky was cloudless, or when only detached clouds were present. The balloon was furnished with means capable only of taking it to such an altitude that it could regain the surface of the sea at a distance which does not exceed the limits of visibility. The ship is then stopped on the spot where the balloon was started, and attentive observers watch all directions in order to detect its return from above the clouds. One experiment of this kind that the Prince made succeeded perfectly, and the balloon, which had reached a height of 15,750 feet on a day when the sky was completely covered by very low clouds, was detected and recovered at a distance of twelve miles.
But the most remarkable results the Prince of Monaco has attained have been with pilot balloons. "These balloons," says the Prince, "which are small enough to be embraced by the arms of a man, have been followed with a special theodolite to the extraordinary altitude of 29,800 metres (97,700 ft.), if it is assumed that their velocity of ascent increased a little with
