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264 number to establish the orbit. The existence of two inner satellites has since been established, and it is probable that Struve's observations were sometimes on one of them and sometimes on the other.

The field covered by Struve's subsequent labors is so large and his papers so numerous that it is not easy to give any untechnical account of his works. He has determined the parallax of several stars, made a careful series of observations on the rings of Saturn, made several journeys to observe solar eclipses, and had general charge of the geodetic operations in the Russian Empire. His greatest recent work has been a continuation of the work of his father on double stars. In 1878 the observations of this class, which he had been making for thirty-five years, were all collected and published in the ninth volume of the "Pulkowa Observations."

In 1862 he succeeded his father as Director of the Pulkowa Observatory. Since that time his energies have been as much occupied with the general direction of the establishment as with independent scientific work. His family has been distinguished by the managing capacity and diplomatic skill of its members, some of whom hold high positions in the civil and diplomatic service of the Government. The subject of our sketch is, in this respect, not inferior to his relatives; and the great efficiency which the observatory has attained under his direction is due as much to his cautious temper, good sense, and judicious management, as to his scientific ability.

The last enterprise undertaken by Struve is of special interest to us. For many years the great telescope at Pulkowa, and its brother instrument at Cambridge, both of fifteen inches aperture, were the largest successful refractors in the world. With the construction of the eighteen-inch telescope for Chicago in 1862, the introduction of larger instruments was inaugurated and continued until the great Washington telescope left that at Pulkowa far behind. This was so far contrary to the ideas of the Pulkowa Observatory that about a year ago the Russian Government authorized Struve to negotiate for the construction of a larger refractor than any yet made. The most difficult and delicate matter was the objective, and, after a visit to the principal European workshops, he determined to come to America for the purpose of conferring with Alvan Clark and Sons, and inspecting their chef-d'oeuvre at Washington. On arriving here in August last he spent several weeks in visiting friends and institutions. At the Saratoga meeting of the American Association for the Advancement of Science, he had an opportunity of making the acquaintance of many of our scientists. The result of his visit to Cambridge was the completion of a contract with the Clarks for a thirty-inch object-glass, which, it is hoped, may be completed within two years if the glass disks can be procured from the makers of optical glass. The mounting of the telescope is to be made by the Repsolds at Hamburg. Having executed his mission, he sailed for his home on September 13, 1879.