2 MR. RUMKER'S OBSERVATIONS 



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 chrono- 

 meter, 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. 



Dip of the Needle observed with a Dipping Compass made by Gambey of Paris. 



In five minutes the Needle made in No- 

 vember 1821, 

 In the magnetic meridian . . 128.0 vibrations. 

 In the magnetic prime vertical 120.8 



Therefore (j^,y = cos dip = 62° 57'. 



By direct Observation. 

 Date. Dip. 



November 1821 62 36 19 



March 21, 1823 62 18 40 



II. Latitude of the Observatory. 



Observations for determining the latitude have not merely a local interest. 

 The differences between the latitudes derived from stars north and south of 

 the zenith, as well as from upper and lower solstices, have long been an object 

 of speculation by astronomers ; so that a series of observations for the latitude 

 of any place on the surface of the earth is valuable : and if the anomalies 

 alluded to should not originate in the defects of the instruments alone, but in 

 hitherto unknown laws of Nature, observations in the Southern hemisphere 

 will be doubly interesting. 



