Our Astronomical Column

Abstract

ASTRONOMY AT THE PARIS ACADEMY, APRIL II.—MM. Périgaud and Boquet have independently made some observations of the latitude of Paris Observatory, one of the objects of the investigation being to determine whether the value underwent a periodic variation. The two series of observations only differ from one another by about one-hundredth of a second of arc; the value derived from them is 48° 50′ 11″˙01. No definite evidence of variability was obtained. Admiral Mouchez, in commenting upon these observations and a discussion of the latitude of the Observatory, made by M. Guillot in 1879, said that doubtless the variation found at other Observatories was wholly or in large part due to the influence of temperature on astronomical refraction. A photograph taken by Dr. Gill was presented by Admiral Mouchez to the Academy. It embraced an area of 2° × 2°, and on this sky-space from 30,000 to 40,000 stars had left their impressions, besides two nebulæ. The exposure given was 3h. 12m. instead of the 1h. which is given to plates for the “Carte du Ciel.” If this exposure were possible for the whole photographic map of the heavens, about 300,000,000 stars would record their existence instead of 30,000,000.