Much has been done within the past century in many other branches of astronomy. I must especially mention the important subject of meteoric showers. For the development of our knowledge of this attractive part of astronomy we are largely indebted to the labors of the late Prof. H. Newton, of Yale. By his investigations, in conjunction with those of the late Professor Adams, it was demonstrated that the shower of shooting stars which usually appears in the middle of November is derived from a shoal of small bodies which revolve around the sun in an elliptic track, and accomplish that circuit in about thirty-three years and a quarter. The earth crosses the track of these meteors in the middle of November. If it should happen that the great shoal is passing through the junction at the time the earth also arrives there, then the earth rushes through the shoal of little bodies. These plunge into our atmosphere, they are ignited by the friction, and a great shower is observed. It is thus that we account for the recurrence of specially superb displays at intervals of about thirty-three years. But one more great astronomical discovery of this century must be mentioned, and here again, as in so many other instances, we are indebted to American astronomers. It was in 1877 that Prof. Asaph Hall discovered that the planet Mars was attended by two satellites. This was indeed a great achievement, and excited the liveliest interest and attention. Since the days when telescopes were first invented all the astronomers have been looking at Mars, and yet they never noticed (their telescopes were not good enough) those interesting satellites which the acute observation of Professor Hall detected with the help of the great telescope of the Naval Observatory at Washington. This discovery was followed by another of a still more delicate nature, when that consummate observer, Professor Barnard, using the great Lick telescope, detected the fifth satellite of Jupiter. This is indeed a most difficult object to observe, requiring, as it does, the highest optical power, the most perfect atmospheric conditions, and the most skillful of astronomical observers. We may take this observation to represent the high-water mark of telescopic astronomy in the nineteenth century. This being so, it may fitly conclude this brief account of some of the most remarkable astronomical discoveries which that century has produced. THE APPLICATIONS OF EXPLOSIVES. BY CHARLES E. MUNROE, PROFESSOR OF CHEMISTRY, COLUMBIAN UNIVERSITY. [Illustration: GUN-COTTON FACTORY. Dipping cotton in nitrating troughs.]