

MAGNETIC LINES OF NO VARIATION. 243 



The remarkable connexion which has been observed 

 between the changes in the physical condition of the 

 surface of the sun. and terrestrial phenomena,, must not 

 escape our notice. Sir William Herschel thought he 

 perceived a link connecting the dark spots 011 the sun's 

 face with the variations of the earth's temperature. 

 This has not, however, been confirmed by the observa- 

 tions which have been made since the time of Herschel. 

 The careful examinations of the solar spots which have 

 been made by Schwabe,* prove a well-defined order of 

 progress in them. He has discovered that they move in 

 cycles of ten years from the smallest number visible in 

 a given year, they regularly increase for five years, 

 when they reach their maximum; they then as regularly 

 decrease, and at the end of another five years they are 

 at their maximum number. The magnetic observation? 

 which have been carried on by the British and othei 

 governments for some years, over every part of the 

 world, have elicited the fact that the order of variation 

 in the earth's magnetic intensity is in cycles of ten 

 years, and the law of increase and decrease which is found 

 to prevail with the solar spots distinctly marks the varia- 

 tions of terrestrial magnetism. Few more interesting 

 facts than this are within the range of our knowledge, 

 proving as it does the direct dependence of terrestrial 

 phenomena on solar force. 



The constancy with which a magnetised needle points 

 along a certain line which varies a little from the earth's 

 axial line, renders it one of the most important instru- 

 ments to the practical and the scientific man. The 

 wanderer of the ocean or of the desert is enabled, 

 without fear of error, to pursue his path, and in un- 

 known regions to determine the azimuth of objects. 



Theory of Terrestrial Magnetism, by Professor Carl Friedrich 

 Gauss, of the University of Gottingen. Scientific Memoirs, 

 vol. ii. p. 188. 



* Humboldt's Cosmos. Ottes translation. 



