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HAND-BOOK OF WASHINGTON. 53 Circles. In another, the Transit instrument; in another, the Prime Vertical Instrument; and in another yet, the Great Kefraction Circle invented by the Superintendent. It was made by Ertel & Son, Munich, and taken altogether is, perhaps, one of the finest instruments any where to be found. Such is the delicacy of its construction, and such the accuracy of its adjustments, and the nicety of its performance, that the heat of the observer’s person, as he approaches it to make an observation, is found to be one of its principal sources of error. But perhaps the most wonderful object at this interesting Establishment is the Electro-Chrono graph, invented by Dr. Locke, of Cincinnati. It is in the room with the Transit Instrument, and is so arranged, by its connexion with an electri cal battery in the building, that its ticks may be heard in any part of the country to which the magnetic wires lead, provided they be put in con nexion with it. Thus it may be made of itself to record the time, and in such a manner, that the astronomer in Boston, New Orleans or else where will know it, and tell the time of day by this clock, as well as one who stands before it and reads the hands on its face. The Observatory regulates the time for Wash-