XXIII. Observations of the comet of Encke, made in June 1832. By Thomas Henderson, Esq., His Majesty's Astronomer at the Cape of Good Hope. Communicated, by Command of the Lords Commissioners of the Admiralty, by Captain Beaufort, R. N., F. R. S., Hydrographer to the Admiralty

Abstract

The following observations (excepting those with the transit instrument,) were made with a circular micrometer, constructed by Simms, and applied to an achromatic telescope of Dollond, forty-five inches in focal length, and three and a half inches aperture, furnished with a portable equatorial stand, which can be adjusted to any latitude. By means of the horary and declination circles, and the difference of right ascension and declination betwixt the comet and the nearest bright star, the telescope was readily pointed to the comet’s place; but when the comet got to the southward of the zenith, and was near the meridian, the equatorial apparatus became useless, as its supports came in the way of the telescope: the telescope was then pointed to the comet according to the best estimate which the eye could make of its place in the heavens relatively to the neighbouring stars. The instrument was placed either at one of the windows of the Observatory building, or out of doors in a corner sheltered from the wind, where the best view of the quarter of the heavens where the comet was situated could be obtained. The magnifying power employed was thirty-two, and the radius of the ring was found to be 1015 seconds of arc. The transit instrument by Dollond is nearly ten feet in focal length, and the object-glass is five inches in diameter. For observing the comet, an eye-glass, magnifying eighty-eight times (the lowest power which it possesses), was used.