Q 
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. 
By direct Observation. 
Date. Dip. 
November 1821 62 86 19 
March 21, 1823 62 18 40 
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 (x') = cos dip = 62° 57 '. 
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. 
