192 



Magnetism of the United States and its Vicinity. 



Art. XVI. — Notice of some recent Additions to our Knowledge 

 of the Magnetism of the United States and its Vicinity; 

 by Eli as Loomis, Professor of Mathematics and Natural Phi- 

 losophy in the University of the City of New York. 



In the forty-third volume of this Journal I have given a dis- 

 cussion of all the observations of magnetic dip in the United 

 States with which I was then acquainted ; and in the forty- 

 seventh volume I have given the comparison of these observa- 

 tions with Gauss's theory. Quite recently we have received a 

 most important addition to our stock of observations, from Major 

 Graham, Prof. Locke, and Capt. Lefroy, published in the Trans- 

 actions of the American Philosophical Society and the Royal 

 Society of London. In order to make the American Journal a 

 complete depository of our knowledge upon this subject, it is 

 proposed to present an abstract of these new observations accom- 

 panied by a few remarks. 



and 



Major Graham were made in the years 

 '45. Those of 1840 were made with a 

 dipping needle constructed by Trough ton and Simms, having a 

 vertical circle eight inches in diameter, graduated to fifteen min- 

 utes. The azimuth circle reads to single minutes by the aid of a 

 vernier. The observations subsequent to 1840 were made with 

 an instrument by Gambey, having a vertical circle ten inches in 

 diameter, and graduated to ten minutes. In conducting the ob- 

 servations, the usual precautions were observed of reversing the 

 poles of the needles, and reading with face alternately east and 

 west. The following is a summary of Major Graham's ob- 

 servations. 



Table I. 



station. 



Uuitude 



Lake Pohenagamook, 

 Beau Lac, 

 Madawaska River, 

 River St. John, 

 Fish River, 

 St. Francis River, 

 Grand River, . 

 Little Blark River, 

 River St. John, 



Falls of St. John, 



Peconk Hill, . 



Big Black River, 



Aroostook, 



Blue Hill, 



River St. John, 



Branch of St. John, 



Park's Hill, . 



Source of St. Croii 



Taschereau's, 

 Moose River, 



Longitude 



77 47 



77 47*5 



77 44 '5 



77 43*5 



77 38-4 



77 4o*5 



77 3i *o 



77 29 '5 



77 32-2 



77 37*5 



77 M 1 



77 18 -i 



77 25 A 



77 24 'o 



77 e 1 ' 6 ! 



76 57*4 



76 5o-4 



76 48*5 



i843 



]843 



1 84 3 

 1 843 



1 843 



1 844 



i843 

 i843 



i843 



2 843 

 1 844 

 1 84o 



i64i 



1 844 



