Page:Popular Science Monthly Volume 11.djvu/559

Rh employed in place of the prisms of his spectroscope a diffraction-grating ruled upon speculum metal by Lewis M. Rutherford, Esq., of New York City. This grating has 4,000 lines to the English inch, and gives a spectrum whose definition leaves nothing to be desired. For the study of the solar prominences such a grating appears to me infinitely superior to any combination of prisms.

Director, M. Respighi; Assistant, M. Scarpellini.—The second observatory in Rome, that of the Capitol, is under the patronage of the Accademla dei Nuovi Lincei. It is placed upon the summit of the southeast portion of the palace of the Capitol, and it is sufficiently removed from the neighborhood of traveled streets to preserve it from the vibrations caused by carriages, etc. The instruments are undisturbed enough to allow of the most delicate astronomical observations, such as the determination of the nadir-point and the observation of stars by reflection from the surface of quicksilver, at all hours of the day.

The horizon is also entirely free, so that if the situation allowed of a more regular placing of the instruments it might be considered as very favorably situated for the making of observations of precision. M. Respighi is now occupied in observations of solar protuberances, and in meridian observations, which are to serve as a basis for a catalogue of stars. For the first purpose an equatorial by Merz, of four and a half inches aperture, and a direct-vision spectroscope with five prisms, are employed.

A beautiful meridian-circle by Ertel serves M. Respighi for his observations of those fixed stars of the first six magnitudes, which are to be employed by the Italian staff-officers in their geodetic operations. This observatory possesses also a reflex zenith-tube, made by Ertel from designs by M. Respighi himself. It is a sort of transit-instrument, with an aperture 108 millimetres (4.25 inches), provided with an eyepiece which contains three groups of declination-wires. The basin of quicksilver, by means of which the reflected stars are observed, is 21 metres (68.90 feet) below the objective, which thus masks but a small portion of the sky. When the telescope is directed toward the nadir stars very close to the zenith may be observed by the declination-wires during their transit; at the same time and without touching the instrument the nadir may also be observed, so that the zenith-distance of each star depends upon the micrometer-screw alone and is determined with the great accuracy which this kind of observation allows.

Assistant, M. William Tempel.—The old observatory of Florence, formerly presided over by Donati, has been dismantled, and a new and magnificent structure is nearly built at Arcetri, near the house formerly inhabited by Galileo. The old observatory is now used for a meteorological station, under charge of Prof Pitti.