Astronomical observations made at the Observatory Paramatta in New South Wales

Abstract

I. Magnetic Observations made at Paramatta. Variation of the Needle observed with Dollond’s Magnetic Transit. For the information of persons who are not acquainted with the nature of the instrument, it is necessary to add that the transit of the sun was observed with the same tube with which, after an application of a microscope, the position of the needle, or magnetic meridian, could be read off the limb surrounding it, whilst three nonii gave the division corresponding to the true meridian on that day. Not considering the magnetic observations of sufficient importance to neglect on their account the observations of the sun with the regular transit and mural circle, I left an assistant to observe its culmination with the magnetic transit; and as this instrument could not be kept permanently in the same position, I directed him to turn the tangent screw of the azimuth circle so as to bring the first wire in contact with the sun’s preceding limb at a second of a chrono­meter, computed for that purpose, with the declination for the interval of wires and semidiameter. For any difference found after the reduction of the wires, a correction of the azimuth remained to be made. With more attention greater accuracy might have been obtained, although the application of the microscope to the tube could not fail of displacing the optical axis.