Observations on atmospherical refraction as it affects astronomical observations; in a letter from S. Groombridge, Esq. to the Rev. Nevil Maskelyne, D. D. F. R. S. Astronomer Royal. Communicated by the Astronomer Royal

Abstract

Mr. Groombridge being in possession of a transit circle four feet in diameter, made by Troughton, undertook a series of observations upon circumpolar stars, for the purpose of determining the latitude of his observatory. As his instrument had the advantage of being fixed upon stone piers, which are not liable to partial expansion, and as the size of the instrument itself seemed to him better adapted to determining the real quantity of atmospherical refraction than any which had been before employed for the same purpose, he extended the range of his observations as low down towards his north horizon as his situation would permit. For this purpose he selected fifty stars of different polar distances, and of these he made, upon the whole, upwards of 1000 observations.