REPORT OF THE SECRETARY. 19 



however, was rendered to the enterprise in this country, except in 

 the instance here referred to, in which the observations were con- 

 ducted by Dr. Bache, at Philadelphia, by means of funds supplied 

 by the members of the American Philosophical Society and the Topo- 

 graphical Bureau of the United States, and with instruments furnished 

 by G-irard College. This series of observations commenced in May, 

 1840, and, with short interruptions, terminated in June, 1845, thus 

 furnishing a record extending over five years, for three or four 

 months of which the observations were made bi-hourly, and for the 

 remainder of the time hourly. A general reduction of these observa- 

 tions was published in 1847, by order of Congress, in three octavo 

 volumes, with an atlas of diagrams. The records, however, contained 

 facts of great interest, which, owing to the laborious duties of Pro- 

 fessor Bache, could not then be deduced from them, and he has since 

 renewed the investigation, with the aid of Mr. Schott, and the present 

 paper gives an account of the first results which have thus been 

 obtained. 



To present the bearing of the interesting researches exhibited in 

 this paper on the progress of science, it may be proper to state that 

 the magnetic force of the earth is almost constantly disturbed, both 

 in direction and intensity. 



1. It is subject to a change which appears to complete its cycle in 

 a large number of years, for the determination of which it is necessary 

 to know the magnetic state of various places on the globe simul- 

 taneously at a given epoch, and again after the lapse of several years. 

 2. It is subjected to a change which is completed in the course of a 

 year; and 3d, another which runs through its course in a single day. 



Beside these regular disturbances, there is another series of varia- 

 tions, large in magnitude, denominated magnetic storms, Avhich have 

 been, until lately, considered as fitful, appearing to observe no law, 

 but which Avere manifest over a considerable part of the earth's 

 surface. These, however apparently irregular as to the individual 

 instances, are in all probability, as has been shown by General Sabine, 

 subject to a law of more frequency of occurrence in certain years. 



The object of Professor Bache 7 s paper is to investigate from the 

 data furnished by the Girard observations, the law of recurrence of 

 •the latter disturbances. Since this has not as yet been accurately 

 ascertained, and every independent series of observations when pro- 

 perly discussed is of great value in giving more precision to our 



