250 



MAGNETIC OBSERVATIONS ON THE BOUNDARY LINE 



MAGNETIC OBSERVATIONS. 



Magnetic observations 

 under the direction 



Mexico 



of Major W. H. Emoi 

 iscussion of the magnet 



in 1855, 



treaty of 

 Mexican 



Boundary Surveys. 



RECOMPUTED 



I. Magnetic observations in 1855. 



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

 beino- tbose at wbich astronomical observations were made in de*rmining 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 determina- 

 tions, as the subjoined abstracts show. 



The declination was obtained by referring the direction of the needle to the astronomical 

 meridian carefully determined 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 Gambey) of superior con- 

 struction. Two needles were used at each of the stations ; and at three of them, viz: Carriza- 

 lillo, Espia, and Los Nogales, the poles were repeatedly reversed, so as to obtain the corrections 



r 



to be a 

 1, and 



+ 



No. 



No 



m 



the following abstract of results : 



Needle No. 1. 



Station. 



Dip. 



No. of sets. 



4 



Initial Point 



Carrizalillo 



££pia. 



Ojo del Perro . . . 

 San Luis Springs 

 San Bernardino. 

 fiaauCruz river 



l*os Nogales 



O } 



68 39 

 58 31 

 67 59 

 57 28 

 57 37 

 57 19 

 57 28 

 57 13 



3 

 3 

 I 

 9 



1 



Needle No. 2, 



Dip. 



No. of sets. 



2 

 1 



58 19 

 68 13 

 57 50 

 57 5 



57 21 



56 58 



57 17 

 57 1 



3 

 3 



9 



3 



1 



Remarks 



Poles reversed in each pet. 



ti 



(C 



cc 



it 



3 



Poles reversed in each set 



The difference of about 16' between the results by the two needles is too large to admit of 



the mean being taken. 



An examination of the pivots having shown some corrosion on a pivot 



be 



of Iso. 2, the probability is that the results by No. 1 are to 



observations with that needle show a greater consistency among themselves. The results by 



No, 1 are therefore adopted in the general table. 



