EARTH'S MAGNETISM TO THE SOLAR AND LUNAR PERIODS. 139 



year ; the diurnal range is gi'eatest in summer, and least in winter.* These re- 

 sults will be found to differ considerably from the following, excepting in the 

 periods for the whole year. 



6. The mean of the vertical component for the year 1844, at Makerstoun, 

 was least at 14'' (Makerstoun mean time) ; it increased gradually, from that time, 

 tUl nearly 21'" ; it then diminished slightly tiU nearly 23'' ; after which it increased 

 rather rapidly till 5'' 30"" ; it then diminished with much rapidity till midnight, 

 increasing slightly from 12'' to 13'', and diminishing slightly again to the minimum 

 at 14'' ; or the vertical component has 



The principal minimum at li' 10°" Makerstoun mean time. 



A secondary maximum at 20' 50°" 



A secondary minimum at 22 50"° 



The principal maximum at 5' 30"° 



Perhaps a third minimum at 12'' 10 



And a third maximum at 13'' 10"° 



The slight inflexion at IS"" (See Mean Curve, No. 1., Plate VI.) would not have 

 been noted as a maximum, but simply as a slight irregularity probably due to dis- 

 tiu*bances, were it not for the evidence which, with one exception, evei-y month in 

 the year gave to the same effect. If, however, it be considered simply as an 

 irregularity (it will be the only one in the whole period), IS"" 10™ must be taken as 

 the actual period of the principal minimum, the vertical component having nearly 

 equal values at 12" 10"" and 14" 10'". 



7. The form of the diurnal curve, and the periods and number of maxima and 

 minima vary throughout the year. Having found that the diurnal curves, for 

 each of the two months symmetrically placed with regard to the solstices, were 

 nearly identical in periods and range, only the mean cuitcs for each couple have 

 been projected (Curves, No. 1, Plate VI.), namely, the means for the months of 



January and December. April and September. 



February and November. May and August, 



March and October. June and July. 



8. The transitions of the periods of maxima and minima throughout these 

 months is curious ; the principal maximum occurs about 6" at the solstices, near 

 4" at the equinoxes, and about 5" at the intermediate periods. The principal 

 minimum occurs about 17" at the winter solstice, about midnight at the equi- 

 noxes, and about noon at the summer solstice. In January and December there 



* Toronto Observations for 1840, 1841, and 1842. Abstracts, &c., p. Ix. The Toronto observations 

 were made every two hours, and the Makerstoun observations every hour. 



