Page:Popular Science Monthly Volume 45.djvu/859

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to observe a transit of Venus. He visited China and Japan on the way. In 1878 he headed an expedition to Colorado to observe the eclipse of the sun, and in 1882 he took a party to Texas to observe another transit of Venus.

Although on these expeditions he did valuable service, it has been at Washington with the twenty-six-inch equatorial that he has done his most important work. He has made studies of many double stars, to determine their distances and motions. He has also given a great deal of time to the study of the planet Saturn. He made an especial investigation of the rings of this planet, and also discovered the motion of the line of apsides of Hyperion, one of Saturn's satellites. But by far the most important discovery he has made, the one that will connect his name with astronomy as long as the planets exist, was his discovery of the satellites of Mars. It had been thought by some old astronomer that perhaps Mars had satellites, but no one had been able to find them. In the fall of 1877 Mars was in a very favorable position to observe, and Prof. Hall turned his big telescope upon it. He searched night after night without finding anything new. He began to give up hope; but on the night of August 11th he discovered a little speck that turned out to be the outer satellite. Six days later he discovered the inner one. The discovery of these two little bodies (the smaller one being not more than fifteen miles in diameter) spread quickly among the observatories. The eager astronomers immediately began to find enough extra moons to supply another solar system. One observer insisted that there was one more moon at least, and Prof. Hall was blamed as stupid for not seeing it. But after a thorough investigation it was shown that Prof. Hall had discovered the two and the only two satellites of Mars,

This important discovery brought his name at once before the world at large, and was not slow in earning its reward. The Royal Astronomical Society presented him with a gold medal, and he was given the Lalande prize from Paris. Since that time his work has been recognized as it should. He has become a member of the most important scientific societies of this country, and an honorary member of the royal scientific societies of England and Russia and of the French Academy. The universities of the country have recognized his work, Yale and Harvard each giving him the degree of LL. D. The very last honor conferred upon him is the Arago medal, just awarded to him by the French Academy of Sciences.

Personally, Prof. Hall is a fine-looking man. He is tall and broad-shouldered. His forehead is high and deep. His eyes are clear and bright, in spite of years spent in gazing at the stars. He has always been strong and healthy. He is fond of the open