132 TERRESTRIAL MAGNETISM. 



of terrestrial magnetism have been made on a uniform system 

 for several years), which has first supplied general and com- 

 plete data. The march of the needle in the middle latitudes 

 of the southern magnetic hemisphere is quite the opposite 

 of its march in the northern hemisphere ; for as in the south, 

 the end of the needle which points towards the south moves 

 from morning to noon from the east towards the west, it 

 follows that the north-pointing end of the same needle is 

 moving at the same time from the west towards the east, 

 contrary to what we have described above as 'its march 

 during those hours in our own hemisphere. 



Sabine, to whom we are indebted for the sagacious dis- 

 cussion of all these variations, has so combined five years 

 of hourly observation at Hobarton (42 53' S. lat., 9 57 

 E. decl.) and at Toronto (43 39' N. lat., 133'W. decl.), 

 that the periods from October to February and from April 

 to August are distinguished from each other, the omitted 

 intervening months of March and September presenting, as 

 it were, transitional phaenomena. At Hobarton the north 

 end of the needle has daily two easterly and two westerly 

 maxima of elongation. ( 163 ) In the portion of the year 

 from October to February, the movement takes place towards 

 the east from 20h. or 21h. to 2h. ; there is then a small move- 

 ment towards the west from 2h. to llh., from llh. to 15h. 

 again to the east, and from 15h. to 20h. the needle returns 

 to the west. In the portion of the year from April to August 

 the eastern turning hours are retarded to 3h. and 16h., and 

 the western turning hours are made earlier, being at 22h. 

 and llh. In the northern hemisphere, the westward move- 

 ment of the needle from 20h. to Ih. is greater when the Sun 

 is in the northern than when he is in the southern signs : 



