DIURNAL VARIATIONS FOR THE VERTICAL COMPONENT OF MAGNETIC FORCE. lv 
Throughout the year, therefore, the greatest effect of disturbance in increasing the vertical component occurs 
near 64 p.m. or about the epoch of the maximum for the mean value, No. 100. 
2d, The greatest effect of disturbance in diminishing the vertical component occurs 
In Dec. Jan. Feb. March, April. May, June. July, Aug. Sept. Oct. Nov. 
About 2» 30™ a.m. 14 40™ aM. 2) 50™ a.m. Q> 45m a.m. 35 30™ a.m. 
The greatest effect in diminishing the vertical component occurs throughout the year between 13" and 33" 
A.M., or rather after the epoch of the principal minimum for the mean value, No. 100. Irregular disturbance, 
therefore, has the same effect on the value of the vertical component as the cause producing the regular diurnal 
variation. 
3d, The effect of disturbance on the vertical component is zero 
In Dec. Jan. Feb. March, April. May, June. July, Aug. Sept. Oct. Nov. 
About 1124. & 93hp.M. 10" am. & 93" pM. 9am. & 10Z4P.M. 102% a.m. & 93" pM. 91" a.m, & 92 P.M. 
The effect of disturbance on the hourly mean appears to be zero about the time the sun is on the magnetic meridian. 
Diurnal Variation of Frequency of the Positive Departures from the Hourly Mean Positions.—The number 
of observations which were in excess of the hourly mean for each month in 1844 and 1845 having been ob- 
tained, the means for groups of months were taken, and the following Table was formed. 
TABLE 52.—Numbers in 100 Observations of the Vertical Component of Magnetic Force which were 
greater than the corresponding Hourly Means, deduced from all the Hourly Observations in 1844 
and 1845. 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
0 
1 
a 
104, The following are the epochs of maximum and minimum frequency of the positive departures for each 
quarter. 
Nov. Dee. Jan, Feb. Mar. April. May, June, July. Aug. Sept. Oct. 
Maximum, 11) p.m.—2h a.m. Qh__4h au, Qh__5h a.m. 11” p.m.—6" a.m. 
Minimum, 5) eM. 5> pm. 5} p.m. 53> pm. 
Tt appears, therefore, that the number of positive departures from the mean of all the observations for the 
hour is least about 55 p.m, or about the time that the effect of disturbance in increasing the hourly mean is 
greatest, and that the number is greatest when the effect of disturbance in diminishing the hourly mean is least, 
No. 103: the effect of disturbance on the hourly mean position is so considerable when compared with the 
whole diurnal variation, that it is evident that the number of departures from the undisturbed positions must 
have their maximum about 5" p.m. and their minimum about 243" a.m. 
Diurnal Variation of the Mean Differences of the Value of the Vertical Component from its Monthly Mean 
Value at the corresponding Houwr.—Table 53 has been formed from Table LIII., for 1844, p- 387, and 
Table XLIII., p. 24 of this volume, in the manner already described, No. 43, for Table 18. 
MAG. AND MET. oBS. 1845 anp 1846. 
