315 



were a sextant of 7^ inches radius, made especially for me by Simms 

 (of the late firm of Troiighton & Simms), of London, divided on pal- 

 ladivm to read by aid of the vernier to ten seconds of arc, with an 

 artifical horizon of mercury, and a good chronometer by Parkinson 

 & Frodsham, of London. The observations were made on Polaris 

 {cc Ursse Minoris), north, and (circum-meridian) on /3 Ononis, south. 

 The results were as follows, viz. 



Latitude of station, by observations on the 20th 

 of January, 1858, 41° 5:3' 53" N. 



Do. by observations of January 21st, 1858, 41 53 54.6 



Mean, - - 41 53 53.8 



By triangulation, based for orientation on the 

 true meridian ascertained with the astronomical 

 transit, the dome of the City Hall or Court House 

 was found to be 4462.49 feet south of the parallel 

 of the observing station; or, in arc, of the meridian, — 44.1 



Latitude of the City Hall or Court House of 

 Chicago (approximate), - - - - - 41 53 09.7 N. 



In the American Almanac for 1858,* the longitude of Chicago is 



given west of Greenwich, ..... 5A. 50m. 20s. 



And the latitude, 42° 00' N. 



Graham & Ashe west of the American Almanac 



for 1858, in the longitude of Chicago, ... + 12s.08 



Graham south of American Almanac for 1858, in 



the latitude of Chicago, ■ - . - - — 6' 50". 3 



The Magnetic Declination at Chicago. 

 This was ascertained on the 23d of July, 1857, by placing a cir- 

 cumferenter, furnished with a transit telescope and with a magnetic 

 needle 4| inches long, upon a station in the true meridian line deter- 

 mined with the astronomical transit. By a mean of four readings of 

 the needle, two with the zero (o) of the azimuth circle north, and two 

 others with it south, the following result was obtained, viz. 



1857, July 23, at 4 o'clock P. ill.— Magnetic declination at Chi- 

 cago (observing station as before), 5° 46' 07^" E. of N. ; or, say 

 five degrees forty -six and one-tenth minutes east of north. 

 Very respectfully yours, &c. &c. 



JAMES D. GRAHAM, 



Meviber of the Societg. 



* See the table of latitudes and longitudes of places, p. 45. 



