504 EDITOR'S NOTES. 



netic equator" in this case to denote a line passing round 

 the globe, and dividing it into two hemispheres which 

 are distinguished apart by the mean diurnal variation 

 having opposite deflections at the same hours throughout 

 the year. On the dividing line there is no mean diurnal 

 variation ; but it is by no means a line without diurnal 

 variation, for in each half year the alternate phases of 

 the semi-annual inequality constitute a diurnal varia- 

 tion of which the range in each day is about 4 minutes, 

 and which takes place every day in the year except 

 about the equinoxes ; the march of the diurnal varia- 

 tion being from east in the forenoon to west in the 

 afternoon when the sun has north declination, and from 

 west in the forenoon to east in the afternoon when he 

 has south declination. As the magnetic equator is re- 

 ceded from on either side towards the middle latitudes, 

 the mean diurnal variation characteristic of the hemi- 

 sphere becomes more and more sensible, producing, with 

 the deflections of the semi-annual inequality, compound 

 phenomena, in which the character of the semi-annual 

 inequality, (consisting of opposite deflections at the 

 same hours in opposite parts of the year,) is preserved, 

 until the amount of deflection at the turning hours of the 

 mean diurnal variation preponderates over that of the 

 semi-annual inequality : when the phenomena pass from 

 the character of equatorial to that of middle latitude 

 stations. St. Helena is an example of the equatorial 

 phenomena; Toronto of the phenomena described as 

 being those of the middle latitudes of the northern 

 hemisphere; and Hobarton of those of the middle lati- 

 tudes of the southern hemisphere. 



The description which has been given of the pheno- 



