54 



m ags i: tic s r i; v e v o p p b n n s v i. v a n i a . 



Magnetic Tour <;/' L834 and 1835, in tfie NbrtJimstern States. 

 (In connection with Prof. Courtenay.) 



'['lie results of the observations for horizontal intensity, as published in Vol. V 

 (new series) of the Transactions of the American Philosophical Society, Tart III, 

 L837, are expressed in relative measure, Philadelphia being taken as unit. It 

 seems to be desirable to present these results, expressed in terms of the absolute 

 scale, and I have, therefore, inserted them here in connection with my other deter- 

 minations. 



From Mr. Schott's collection of intensities we have, at New York (Columbia 

 College), in IS'2'2, the intensity 3.981 (Col. Sabine observer); and in 1841, in the 

 same locality, 4.01s (Dr. Locke observer); whence the horizontal intensity in 1835 

 is 4.006, from which wc obtain for Philadelphia, in 1835, the value 



1.00000 



4.006 X 



r- = 4.23 



0.941(C) 



In 1836, the value found was 4.16; the mean of these determinations I have 



adopted as the nearest value that can at present be assigned, viz., 4.195. 

 We have, accordingly, the following table of results : — 



1S34— 35. 



Philadelphia, ]s:;i_r, 



Wesl Point, 



\ru York, " 



Newport, 11. I., is:;:, 



Providence, K. I.. " 

 Springfield, Mass., 



Albany, N.Y., " 



That the value adopted tor Philadelphia is very nearly correct (and will not 

 hear diminution), may be inferred from the following comparison and the known 

 law of secular change of the horizontal intensity. The comparison is obtained 

 from Mr. Schott's collection : — 



A i West Point. 



1 835 Bache & < lourtenay 



is 12.;, Lefroy . 



x. 



:; 866 

 :: 881 



