THE 



AMERICAN 



JOURNAL OF SCIEICE AND ARTS. 



• 



[SECOND SERIES.] 



Art, I. — On the General Distribution of Terrestrial Magjtetism in 

 the United States^ from observations made in the U, S. Coast Sur- 

 vey and others; by A. D. Bache, Superintendent, and J. E, 

 HiLGARDy Assistant U, S. Coast Survey. With two maps. 



During tlie progress of the Coast Survey witLin tlie last 

 twelve years, observations of the magnetic elements have been 

 made, under special, instructions from the Superintendent, at 

 most of the astronomical stations, and near many capes and har- 

 bors where a knowledge of the variation of the compass was 

 requisite for the use of navigation. The number of magnetic 

 stations now amounts to about one hundred and sixty, distribu- 

 ted (irregularly as yet) along the entire seacoast of the United 

 States, on a great portion of Avhich magnetic observations were 

 now made for the first time. The object of this paper is to de- 

 duce from the Coast Survey observations, in connection with 

 others of recent date, the general distribution of terrestrial mao*- 

 netism in the United States, as far as the data available will war- 

 rant the conclusions. 



These observations have been discussed from time to time 

 under the immediate direction of the Superintendent of the 

 Coast Survey, with the double purpose of determining the dis- 

 tribution of magnetism in different parts of the United States 

 and the local irregularities. Observations have also been re- 

 peated at many places where the discrepancies indicated the ne- 

 cessity for such a course, and generally resulted in throwing the 

 discrepancy upon the existence of local attraction. 



SECOND SERIES, VOL. XXIV, NO. 70. — JULY, lSi7* 



1 



