250 



General Sabine — Comparison of Magnetic [May 26, 



geographical positions, as taken from M. Gauss's ' Allgemeine Theorie/ 

 being, in America, lat. 55°, long. 263° E., and in Siberia lat. 71°, long. 

 1 1 6° E. Combining then the expectation expressed in the Report of " a 

 probable connexion existing between the casual and transitory magnetic 

 variations and the general phenomena of terrestrial magnetism," with 

 M. Gauss's conclusion from the Gottingen researches, that '^the sources 

 of the magnetic disturbances in Europe might possibly be successfully 

 sought in parts of the globe to the north or to the north-west of the 

 European continent," it seemed reasonable to anticipate that a connexion 

 might be found to exist between the " points of origin" of the disturb- 

 ances, if these could be more precisely ascertained, and the critical locali- 

 ties of the earth's magnetism above referred to. To put this question 

 to the test, the first step was to ascertain in a more satisfactory way 

 than had been previously attempted, the laws of the disturbances 

 themselves. The process by which a portion of the observations ex- 

 hibiting the effects of the disturbing action in a very marked degree 

 may be separated from the others, and subjected to a suitable analysis 

 for the determination of their general laws, has been fully described else- 

 where. The immediate effect of its application was to show that, casual 

 and irregular as the disturbances might appear to be in the times of their 

 occurrence, they were, in their mean effects, strictly periodical phenomena, 

 characterized by laws distinct from those of any other periodical phenomena 

 with which we were then acquainted, and traceable directly to the Sun as 

 their primary source, inasmuch as they were found to be governed every- 

 where by laws depending upon the solar hours. To those who are familiar 

 with the theory by which the passage of light from the sun to the earth is 

 explained, an analogous transmission of magnetic influences from the sun 

 to the earth may appear to present no particular difficulty. It is when 

 the influences reach the earth that the modes of their reception, distribu- 

 tion, and transmission are less clearly seen and understood ; but these are 

 within our own proper terrestrial domain and sphere of research ; and ac- 

 cordingly it was to these that the author's attention was directed. Where- 

 ever the disturbances had been observed and were analyzed, it was found 

 that those of the declination were occasionally deflections to the east and 

 occasionally deflections to the west of the mean position of the magnet, 

 and those of the horizontal and vertical forces occasionally increased and 

 occasionally diminished the respective forces. The disturbances of each 

 element were therefore separated into two categories, according as they be- 

 longed to one or to the other class. Each category was found to present 

 diurnal progressions, of systematic regularity, but quite distinct from one 

 another, and so far in accordance with M. Gauss's inference of the existence 

 of various forces contemporaneously in action, independent of one another, 

 and having different originating sources. Confining our view, for simplicity, 

 to one alone of the elements, viz. the declination, its two categories (of 

 easterly and of westerly deflection) presented, wherever they were examined. 



