The Uses of Astronomy | Page 7

the latter, the new instrument at Greenwich, recently erected under the superintendence of the Astronomer Royal. That instrument registers observations in single seconds; the Dudley instrument will register to tenths of seconds. That has six or eight microscopes; this has four. That has a gas lamp, by the light of which the graduations are read off; the Albany instrument has no lamp, and the Doctor considered the lamp a hazardous experiment, affecting the integrity of the experiment, not only by its radiant heat but by the currents of heated air which it produces. The diameter of the object-glass of the Albany instrument is 7-1/2 French inches clear aperture, or 8 English inches, and the length of the tube 8 feet. He would have preferred an instrument in which the facilities of manipulation would have been greater, but was hampered by one proviso, upon which the Trustees of the institution insisted--that this should be the biggest instrument of its kind; and the instruction was obeyed. The glass was made by Chance, and ground by Pistor himself. The eye-piece is fitted with two micrometers, for vertical and horizontal observations. Another apparatus provides for the detection and measurement of the flexure of the tube. Much trouble was experienced in securing a good casting for the steel axis of the instrument. Three were found imperfect under the lathe, and the fourth was chosen; but even then the pivots were made in separate pieces, which were set in very deeply and welded. Dr. Gould said he had been requested by the gentlemen who had this enterprise in charge to suggest, as a mark of respect to a gentleman of Albany who was a munificent patron of Science, that this instrument be known as the Olcott Meridian Circle.
WHAT THE DUDLEY OBSERVATORY IS.
It stands a mile from the Capitol, in the city of Albany, upon the crest of a hill, so difficult of approach, as to be in reality a Hill of Science. There are two ways of getting to it. In both cases there are rail fences to be clambered over, and long grass to wade through, settlements to explore, and a clayey road to travel; but these are minor troubles. The elevation of the hill above tide-water is, perhaps, 200 feet; its distance from the Capitol about a mile and a half. The view for miles is unimpeded; and the Observatory is belted about with woods and verdant lawns. There could not be a finer location or a purer air. The plateau contains some fifteen acres.
The Observatory is constructed in the form of a Latin cross. Its eastern arm is an apartment 22 by 24 feet, in which the meridian circle is to be placed. The western arm is a room of the same dimensions, intended for the transit instrument. From the north and south faces of both rooms are semi-circular apsides, projecting 6 feet 6 inches, containing the Collimator piers and the vertical openings for observation. The entire length of each room is, therefore, 37 feet. In the northern arm are placed the library, 23 feet by 27 feet; two computing rooms, 12 feet by 23 feet each; side entrance halls, staircases, &c. The southern arm contains the principal entrance, consisting of an arched colonnade of four Tuscan columns, surrounded by a pediment. A broad flight of stone steps leads to this colonnade; and through the entrance door beneath it to the main central hall, 28 feet square, in which are placed (in niches) the very beautiful electric clock and pendulum presented by Erastus Corning, Esq. The center of this hall is occupied by a massive pier of stone, 10 feet square, passing from the basement into the dome above, and intended for the support of the great heliometer. Directly opposite the entrance door is a large niche, in which it is proposed to place the bust of the late Mr. Dudley. Immediately above this hall is the equatorial room, a circular apartment, 22 feet 6 inches in diameter, and 24 feet high, covered by a low conical roof, in which and in the walls are the usual observing slits. The drum, or cylindrical portion, of this room is divided into two parts--the lower one fixed, the upper, revolving on cast-iron balls moving in grooved metal plates, can command the entire horizon.
The building is in two stories--the upper of brick, with freestone quoins, impost and window and door dressings, rests upon a rusticated basement of freestone, six feet high. The style adopted is the modern Italian, of which it is a very excellent specimen. The building has been completed some time; but, in consequence of the size of the instruments now procured being greater than that originally contemplated, sundry alterations were required in the Transit and Meridian Circle rooms. These consist of the semi-circular