LATITUDE OF ANNAPOLIS. 135 



ARTICLE VIII. 



The Latitude of Annapolis. — By Hector Humphreys, D. D. 

 President of St. John's College. 



[Read before the Academy, April 27, 1837.] 



The methods adopted for the determination of the latitude at 

 St. John's college, have been, 1st, by meridian altitudes of the 

 sun, and of known stars, south of the zenith ; 2d, by altitudes of 

 Polaris, at the upper and lower culminations, and at the greatest 

 eastern or western elongation ; 3d, by altitudes of any well 

 known stars, taken at distances from the meridian, ascertained 

 by the most exact rate of a well regulated time-keeper ; and 

 4th, by Professor Bessel's rule, for the transit of a star across 

 the Prime Vertical, east and west of the meridian. The baro- 

 meter is placed in the spacious hall of the college, in which 

 the air is not affected by artificial heat, at an elevation of fifty- 

 six feet above the mid-tide, in the Chesapeake bay. The 

 external thermometer, is placed in the shade, out of the build- 

 ing ; and both instruments, are well secured against distur- 

 bance by accidents. The time, has been found, occasionally, 

 by observing the sun, with an excellent sextant and mercury 

 horizon ; but, generally, from altitudes of two stars, near the 

 Prime Vertical, at the east and west, taken on the same even- 

 ing. The most frequent method, has been, to observe only a 

 single star, while in the best position, with a theodolite, taking 

 two altitudes, with the face of the instrument, in its natural 

 position, and two others, in the reversed position of the tele- 

 scope and of the vernier plate. The time has, also, been 

 obtained by meridian transits, using the theodolite for the pur- 

 pose. The instruments, were a fifteen inch repeating theodo- 

 lite, by Troughton, reading to five seconds, and a six inch one, 

 by the same artist, reading to twenty seconds. The first 

 mentioned, is mounted like a transit instrument, and was 

 placed in the plane of the meridian, by passages of Polaris and 

 of Beta, in Cassiopeia, and then verified by transits of other 

 circmnpolar stars. To avoid exposure to the open air, an un- 

 occupied room was taken, affording a view of objects at the 

 north and south ; and meridian marks were made at conside- 



