1. Readings. 



Dip. 



40 



70^ 35.7 



40 



20.0 



80 



27.8 



160 



70 27.7 



302 • OBSERVATIONS OF THE 



Date. Hour. Needle. 



1841, Oct. 5, 3—5, P. M. No. 1, 



" " No. 1, poles reversed, 



" " Mean of No. 1, 



Mean of both sets of observations, ..... 



I have always taken the greatest pains to preserve my compass and needles 

 free from injury; nevertheless, in travelling a great distance by public convey- 

 ances, especially in a new country, some exposure seems unavoidable. The 

 mean results with the two needles agreed very well down to September 22d, 

 at Alton, since which time the results with No. 2 have been quite anomalous. 

 At Edwardsville and Bunker Hill the dip by No. 2 was 11.'. 4 greater than 

 with No. 1, and at Monticello 7'. 3 less. At Cincinnati the difference was still 

 greater, so that from this time I discarded No. 2 altogether. These anomalies 

 I ascribe to rust upon the axis. It was not great, but distinctly visible by a 

 magnifier. I have alluded to such an imperfection in my former paper, p. 67. 

 This rust had doubtless increased during the exposure of the present journey. 

 I have detected no such imperfection in No. 1, and perhaps its indications 

 alone, since September 22d, would be more trustworthy than when united 

 with those of No. 2. 



Magnetic Dip at Columbus, Ohio. Latitude 39° 57' N.; Longitude 83° 3' W. 



Place of observation ninety rods east of the new State House yard. 



Date. Hour. Needle. No. Readings. Dip. 



1841, Oct. 7, 2—3, P. M. No. 1, 40 70° 57'.4 



" " No. 1, poles reversed, 40 70.5 



" " Mean of No. 1, 80 71 4.0 



Observations repeated ten rods farther east. 



Date. Hour. Needle. No. Readings. Dip. 



1841, Oct. 7, 3— 4, P.M. No. 1, 40 70° 69'.7 



'« " No. 1, poles reversed, 40 57 .1 



» " Mean of No. 1, 80 63.4 



Mean of both sets of observations, 160 71 3 .7 



Magnetic Dip at Hebron, Ohio. Latitude 39° 59' N.; Longitude 82° 29' W. 

 Place of observation a hundred rods north of the stage house. 



Date. Hour. Needle. No. Readings. Dip. 



1841, Oct. 8, 1—2, P. M. No. 1, 40 71° 8'.2 



" " No. 1, poles reversed, 40 11 .3 



" « Mean of No. 1, 80 9.8 



