The Meridian Circle and Transit instrument were ordered from Pistor & Martins, the celebrated manufacturers of Berlin, by whom the new instrument at Ann Arbor was made. A number of improvements have been introduced in the Albany instruments, not perhaps all absolutely new, but an eclectic combination of late adaptations with new improvements. Dr. Gould made a distinction of modern astronomical instruments into two classes, the English and the German. The English is the massive type; the German, light and airy. The English instrument is the instrument of the engineer; the German, the instrument of the artist. In ordering the instruments for the Albany Observatory, the Doctor preferred the German type and discarded the heavier English. He instanced, as a specimen of 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.