ANNUAL VARIATIONS OF THE TOTAL MAGNETIC FORCE. lxv 
The winter lunations for 1844 agree with this result, in having a minimum immediately after the inferior 
transit, but not otherwise; this difference, it is considered, is due to disturbances. (See No. 80.) 
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ToTaAL MAGNETIC FORCE. 
133. Absolute Value of the Total Magnetic Force.—The absolute value of the total magnetic force de- 
duced from the value of the horizontal component, and the magnetic dip, as in No, 81, is as follows :— 
Total magnetic force at Makerstoun for the mean epoch 1845 = 10-5267. 
134. Secular Change of the Total Magnetic Force —The determination of this depends chiefly on the balance 
magnetometer, and it is probable that the secular change from that instrument is not to be trusted (No. 84); 
indeed it is probable that the total force remains nearly constant, and this is the more likely the nearer the 
secular change deduced for the magnetic dip is considered to be to the truth. (See No. 116.) 
135. Effect of Disturbance on the Yearly Mean Value of the Total Magnetic Force-—By Nos. 54 and 85, 
we find that the yearly mean deduced from the selected undisturbed days, is greater than that obtained from all the 
observations by 0:000045, the total force here and in the following discussions being considered equal to unity. 
136. Annual Period of the Total Magnetic Force.—This result depends chiefly on that for the vertical com- 
ponent and is entitled to the same weight. The following are the variations of the monthly means of the total 
force, deduced from the observations of the balance and bifilar magnetometers for the four years 1843-6. 
(See Nos. 56 and 87.) 
Prefix. 
0-000 
Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dee. 
+099 —013 —074 —075 —034 +4120 +4052 —001 -—049 —087 +011 4048 
From these numbers, the total magnetic force at Makerstoun is a maximum about the solstices, and a minimum 
immediately after the equinoxes ies Plate VI.) 
137. The monthly means deduced from all the hourly observations in 1844 and 1845, were greater (+) or 
less (—) than those obtained from the days selected as nearly free from disturbance by the following quantities. 
(See Nos. 57 and 89.) : 
Prefix. Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dee. 
0-000 | —069 +001 —106 —060 —062 —003 —037 —061 —052 —078 —008 +002 
The effect of disturbance on the monthly mean was nearly zero in the months of February, June, and 
December, and it was greatest in March and October. When these numbers are subtracted from those in 
No. 136 it is found that the annual period obtained from the undisturbed days in each month, has the same 
epochs as that obtained from all the days. 
138. Annual Variation of the Ranges of the Monthly Mean Diurnal Variation of the Total Magnetic 
Force. The following are the ranges of the mean diurnal variation for each month, as obtained from Table 62, 
deduced from four years’ observations. 
Prefix. | Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Novy. Dec. 
0-000 ! 319 291 612 821 701 546 663 738 715 521 443 298 
The diurnal range of the total force was least in the three months, December, January, and February, and it 
was greatest in April and August: the ranges for March and September were greater than the range for June. 
The following are the ranges of the mean variations obtained from the selected days of 1844 and 1845. 
Prefix. 
0-000 
Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dec. 
112 151 277 398 489 449 448 389 409 321 176 154 
The range of the nearly undisturbed mean diurnal variation was least in January 1844-5, and it was 
greatest in May, but it is probable that the range is nearly constant while the sun is north of the equator, and 
that the differences exhibited here are due to the greater or less amount of disturbance remaining in the 
selected days. (See Nos. 92 and 93.) 
139. Variations of the Daily Mean Total Magnetic Force, with Reference to the Moon’s Age.—The fol- 
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