142 TERRESTRIAL MAGNETISM. 



quent.( 177 ) The analysis of six years of observation at the two 

 opposite stations of Toronto and Hobarton, has conducted 

 Colonel Sabine to the remarkable result, that in both 

 hemispheres, not only the number of disturbances, but also 

 the amount of average diurnal variation from the mean 

 or normal place and the latter (obtained from all the obser- 

 vations of the year omitting the 3469 storms), increased gra- 

 dually in the five years from 1843 to 1848, from 7''65 to 

 10'-58; and that simultaneously with this .a similar increase 

 could be traced in the variations of the inclination and of the 

 total force. This result gained a yet higher degree of impor- 

 tance when he found both a confirmation and a generalisation 

 of it in Lament's detailed investigation of Sept. ] 851, "on a 

 decennial period presented by the diurnal movement of the 

 declination needle." According to observations at Gottingen, 

 Munich, and Kremsmiinster, ( 178 ) the mean amount of the 

 diurnal variation of the declination was at a minimum from 

 1843 to 1844, and at a maximum from 1848 to 1849. 

 After the declination has increased five years, it decreases 

 for the same number of years, as is shown by a series of 

 observations which lead back to a maximum in 17864-.( 1?y ) 

 In order to find a general cause for such a periodicity 

 in all the three elements of terrestrial magnetism, one is 

 inclined to have recourse to some cosmical connection. 

 Such a connection is found, according to Sabine's con- 

 jecture,^ 80 ) in the variations which take place in the photo- 

 sphere of the Sun, i. e. in the luminous gaseous envelopes 

 of the dark solar orb ; for, according to Schwabe's researches, 

 extending over a long series of years, the periods of greatest 

 and least frequency of the solar spots coincide perfectly with 

 those discovered in the variations of terrestrial magnetism. 



