
EARTH’S MAGNETISM TO THE SOLAR AND LUNAR PERIODS. 139 
year ; the diurnal range is greatest 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, 
till nearly 21"; it then diminished slightly till 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 14" 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 infiexion at 13" (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- 
turbances, were it not for the evidence which, with one exception, every 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), 13" 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 curves 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.lx. The Toronto observations 
| were made every two hours, and the Makerstoun observations every hour. 
