318 OBSERVATIONS OF THE MAGNETIC DIP 



turning- of the vertical circle. This, however, is a matter of very secondary 

 importance, the spirit level attached to the instrument, being in all cases to be 

 scrupulously consulted; and, I trust this will be shown by the results of my 

 observations, compared with others. 



During my late visits to the northern lakes and return, I was accompanied 

 by my friend Professor Ducatel, who assisted me in recording the observa- 

 tions. We were both, very particular in the selection of the stations of 

 observations, retiring at convenient but sufficient distances from towns, set- 

 tlements, or large establishments, and always consulting the geological for- 

 mation of the surrounding country and spot. I need not say that we were 

 also very particular as to the removal from our persons of all iron or steel, 

 under any form whatever. 



I. Magnetic Dip at Philadelphia. Latitude 39° 57' 8" N.; Longitude 75° 11' 31" West of 



Greenwich. 

 Place of observation the Girard College. 



Date. Hour. Needle No. ]. Needle No. 2. 



1841, April 26, 4—6, P. M. Observed dip with Poles direct, 71° 55' .1 71° 54' .7 



" «• " Poles reversed, 63 .4 59 .6 



Mean dip, 71 59.25 71 57.15 



Mean dip of both needles, 71 58.20 



These observations were made by Professor A. D. Bache, of Philadelphia, 

 before sending the instrument to me in Baltimore, by way of comparison. 



II. Magnetic Dip at Baltimore, Maryland. Latitude 39° 17' 55" N.; Longitude 76° 37' 50" W. 

 Place of observation, the second square N. E. of the Washington Monu- 

 ment. (The station of observation of Professor A. D. Bache.) 



jjj^tg Hour. Needle No. 1. Needle No. 2. 



1841, April 28, 9— 12, A. M. Observed dip, Poles direct, 71° 33'.00 71° 38'.75 



u a «« Poles reversed, 36 .75 31 .00 



Mean dip, 71 34.87 71 34.87 



Mean dip of both needles, 71 34 .87. 



III. Magnetic Dip at Baltimore, Maryland. 

 Place of observation the Botanical Garden of St. Mary's College. 



Date. Hour. Needle No. 1. Needle No. 2- 



1841, April 28, 3—6, P. M. Observed dip, Poles direct, 71° 4r.37 71° 35'.37 



u " '« Poles reversed, 33 .87 43 .75 



Mean dip, 71 37 .62 71 39 .56 



Mean dip of both needles, 71 38 .59 



