OBSERVATIONS 



MADE IN THE 



YEARS 1845, M6, AND '47, TO DETERMINE THE MAGNETICAL DIP AND DECLINATION, AND 

 INTENSITY OF MAGNETICAL FORCE IN SEVERAL PARTS OF THE UNITED STATES. 



The Observations here recorded form part of a series commenced in 1838, and 

 continued annually for ten years. The results, from 1838 to 1844, inclusive, were 

 published, in 1846, in the "Transactions of the American Philosophical Society." 



The first paper on the subject, read to that Society April 19, 1844, is prefaced 

 by some popular definitions of the elements of terrestrial magnetism, and by an 

 account of the instruments used in making the observations. To this preface the 

 reader is referred for the proper beginning of the subject to which the present pages 

 form a continuation. But as my researches have since been, to a considerable 

 extent, incorporated by Col. Sabine in his " Contributions to Terrestrial Magnetism," 

 they have received additional value and interest by being now connected with other 

 labors of the same kind throughout the enlightened world. It seems, therefore, 

 not improper to quote so much of that paper as may show the degree of confidence 

 to be placed in my results, and the basis upon which rests their connection with 

 similar observations in this and other countries. 



Corres2)onding Observations. — It so happened that Cajit. Lefroy, R. A., in his 

 magnetic researches, chiefly confined to the British Provinces of North America, 

 made observations at several stations which were, unknowingly, occupied by my- 

 self, either before or after him. They were made with different instruments, and 

 at different temperatures, and could be compared only after proper corrections and 

 reductions. We both communicated our observations, independently of each other, 

 to Col. Sabine, who reduced and compared them with very satisfactory results as 

 regards their correspondence and the mutual support which they afford to each 

 other. I copy the following from Col. Sabine's " Contributions to Terrestrial Mag- 

 netism," published in the " Philosophical Transactions" for 1846. 



" Total Intensity as observed hy Capt. Lefrot and Dr. Locke 



at Stations nearly 



'dentical. 



Station. 



Observer. 



Mag. force. 



Observer. 



Mag. force. 



Detroit .... 



Lefroy 



1.814 



Locke 



1.815 



Toronto 









Lefroy 



1.836 



Locke 



1.836 



Princeton 









Lefroy 



1.783 



Locke 



1.783 



Albany 









Lefroy 



1.797 



Locke 



1.792 



New York 









Lefroy 



1.769 



Locke 



1.781 



New Haven . 









Lefroy 



1.773 



Locke 



1.773 



Cambridge 









Lefroy 



1.777 



Locke 



1.774 



Washington' 









Lefroy 



1.772 



Locke 



1.773 



Washington^ 









Lefroy 



1.778 



Locke 



1.800 



Baltimore 









Lefrot 



1.782 



Locke 



1.784 



* Grounds of the Capitol. 



Magnetic Observatory. 



