242 
MAGNETIC SURVEY IN NORTH AMERICA. 
of the United States, (Commissioner for exploring the North-Eastern Boundary of the 
United States under the act of Congress of July 20th, 1840, Principal Astronomer 
and Head of the Scientific Corps on the part of the Government of the United States 
for the joint survey and demarcation of the Boundary under the Treaty of Wash- 
ington,) for the results of observations of the Inclination made from 1841 to 1845 
at thirty-eight stations, chiefly in the parts of the country in which the Boundary 
Commissioners have been engaged. These observations were made with an incli- 
nometer by Gambey, with the exception of three stations, where an instrument of 
Troughton and Simms was employed* ; they appear to have been made with extreme 
care, and the results are remarkably accordant and satisfactory. Major Graham’s 
observations have a particular value, in placing beyond question the fact that the 
direction of the isoclinal lines in that part of the American Continent is to the north- 
ward of east, whilst in the whole range of country elsewhere comprehended in this 
survey, these lines have a direction more or less from the northward of west to the 
southward of east : the geographical position in which certain of the isoclinal lines 
attain their greatest southing is thus satisfactorily ascertained. Major Graham states 
that the results now communicated are abstracted from a paper which has been pre- 
sented to the American Philosophical Society of Philadelphia, and which will be here- 
after published in the Transactions of that Society. 
From Dr. Locke of Cincinnati I have received the result of a very extensive series 
of observations of the Inclination and Force, on which he has been engaged for eight 
years (1838 to 1845 inclusive), comprehending the determination of both elements at 
about 100 stations, distributed in longitude from the geaboard of the United States 
to the Mississippi River, and in latitude from 38° to 48°. It is in fact a magnetic 
survey of the Inclination and Force over the north-western and north-eastern States 
of the Union, conducted by an individual on his own unaided resources, and is one 
of the many notable instances of private research elicited by the impulse and syste- 
matic direction which have been given of late years to the study of terrestrial mag- 
netism. The full account of these observations is designed to be published in the 
Transactions of the American Philosophical Society; but in the mean time the re- 
sults have been spontaneously communicated to me by Dr. Locke (with whom I had 
not previously the pleasure of being acquainted), with full permission to make such 
use of them as I might deem advantageous to science. The Inclinations were ob- 
served with an inclinometer made by the late Mr. Robinson, and the variations of 
the magnetic Force by a Hansteen’s apparatus, in which the needles vibrate in a 
partial vacuum, according to the plan devised by Dr. Alexander Dallas Backe. 
To Dr. A. D. Bache, Director of the Coast Survey of the United States, and to James 
Renwick, Esq., late Commissioner for Surveying and Exploring the North-Eastern 
Boundary of the United States, I am indebted for observations of the Inclination and of 
the absolute horizontal Force, which have been made by direction of the Government 
* These stations were the Military Academy, West Point, New York ; near the monument for marking the 
source of the River St. Croix ; and Park’s Hill on the boundary of Maine and New Brunswick. 
