liv GENERAL RESULTS OF THE MAKERSTOUN OBSERVATIONS. 
the latter occurring about 7" a.m., which is nearly the epoch of a maximum in the other months: in the months 
from March to September the diurnal curve is double, the maxima having nearly the same value in each 
month, and the minima also being nearly equal ; the form of the diurnal curve from March to September is 
nearly constant ; in October the morning maximum becomes less marked, and it wholly disappears in Novem- 
ber. In June the minima oceur almost exactly at apparent midnight and noon, that at the latter time being 
on the whole best marked; the maxima occur when the sun is near the prime vertical. 
102. Diurnal Variation of the Effect of Disturbance on the Mean Vertical Component.—The following 
Table contains the mean effect of disturbance upon the hourly means in each group of months, the assumption 
being made that the effects of disturbance upon the means of the groups of months are zero ; it will be seen 
from Nos. 89 and 85 that the means of the days selected as free from disturbance, are rather greater 
than the means for all the days ; while this difference may be partially due to regular laws, it is also so small, 
compared with the actual differences in the following Table, that the epochs for the zero of effect would 
be little altered if it were taken into account. It will be seen also that the epochs for each group vary little, 
though the effect of disturbance, as found No. 89, differs considerably in the different groups; thus, for the 
group December to February, the mean for all the selected days is 0000005 greater than the mean for all the 
days, while the mean of the selected days in March and April is 0:000061 less than the mean for all. 
TABLE 51.—Differences of Disturbed and Undisturbed Diurnal Variations of the Vertical Com- 
ponent of Magnetic Force, as deduced from Tables 49 and 50, exhibiting the effect of Irregular 
Disturbance on the Hourly Mean Positions. 
Dec. | March. Be Twelve 
hay April. s.| 4 Months. 
00 
| —0057 
| —0052 
|| —0073 
| —0067 
—0059 
—0055 
— 0038 
— 0022 
—0021 
—0011 
| —0010 
+0001 
+0006 
+0014 
+0024 
+0051 
+0062 
+0094 
+0109 
+0096 
+0068 | 
+0022 
| —0019 
| —0050 | 
KBECOnDNAUHRWNHS 
— 
103. The following are the conclusions from Table 51. 
lst, The greatest effect of disturbance in increasing the vertical component occurs 
In Dec. Jan. Feb. March, April. May, June. July, Aug. Sept. Oct. Nov, 
About 6" 15™ p.m, 6h Om p.m, 6» 30™ p.m. 6" 0™ p.m. 5» 30™ p.m. 
