﻿IV. 



Magnetic Observations on the Boundary Line between the United States and Mexico, 

 made in 1855, under the Direction of Major W. H. Emory, United States Commis- 

 sioner under the Treaty o/1853; and General Discussion of the Magnetic Observa- 

 tions made in Connection tvith the Mexican Boundary Surveys. 



Recomputed by J. E. IIILGARD, U. S. Coast-Survey. 



( With a Map.) 



{Communicated September 8, 1856.) 



I. Magnetic Observations in 1855. 



Observations of declination, dip, and absolute horizontal intensity were made at 

 eight stations, being those at which astronomical observations were made in determin- 

 ing the boundary between the United States and Mexico, under the treaty of 1853. 

 The magnetic observations were intrusted to Mr. Marine T. W. Chandler, who succeeded 

 in obtaining very complete determinations, as the subjoined abstracts show. 



The declination was obtained by referring the direction of the needle to the astro- 

 nomical meridian carefully determmed for the survey of the line. The needle of a 

 goniometer by Young was found to show a fair mean of five good needles of different 

 lengths, and was therefore relied on at subsequent stations. The results are given in 

 the general table below. 



Observations of inclination were made with a ten-inch dip-circle by Gambcy, of supe- 

 rior construction. Two needles were used at each of the stations ; and at three of them, 

 viz. Carrizalillo, Espia, and Los Nogales, the jjoles Avere repeatedly reversed, so as 



VOL. vx. NEW series. 28 



