ان DEA‏ و ور بر 
MAGNETIC OBSERVATIONS. 
The instrument, with which the following observations were made, was constructed by W. 
George, of Falmouth, England, under the immediate direction of Mr. Fox, for the use of Col. 
J. D. Graham, of the corps of Topographical Engineers, upon the survey of the N. E. bound- 
ary. Afterwards, under the direction of Major W. H. Emory, of the same corps, it was used 
by me upon the Isthmus of Panama, and in California upon the survey of the Mexican boundary. 
Before and after this trip, in order to determine the changes which might take place in the con- 
dition of the needles, Prof. Bond and myself made several complete sets of observations with 
this instrument at Harvard College observatory. It was then again transported across the 
continent upon the boundary survey, observations being taken at Galveston, at Indianola, and 
at very numerous camps, upon the march, via El Paso, to the Pacific. From San Diego it was 
taken to San Francisco and Sacramento city, and then carried back to El Paso, verifying upon 
the way many of the results previously obtained. Those observations I made with great care. 
They form a portion of the results belonging to the Mexican Boundary survey. When com- 
bined with the other material, of a similar character, collected by Major Emory upon the same 
work, and by Col. Graham upon the N. E. Boundary survey, they will, in connexion with the 
following, form data for a determination of the magnetic elements over a considerable portion 
of North Ain 
This instrument, which I left at El Paso, was loaned by the Hon. Secretary of the Interior 
for the Pacific Railroad survey, and was placed in charge of Lieut. J. C. Ives, Topographical 
Engineers, for use upon our route, near the 35th parallel, from Rio Grande to the Pacific. 
After the performance of this trip it was again, through the kindness of Professor Bond, tested 
by observations at the Cambridge observatory; thus enabling us to place confidence in the long 
series of results obtained with it. 
For the following field observations I desire to give due credit to Lieut. Ives. "Those who 
understand the persevering industry required in such operations, cannot fail to appreciate the 
value of his services in this branch of science. 
