Vertical Component of Magnetic Foece. 



385 



These differences give tlie same law as the differences discussed above. The maximum positive effect 

 occurs about 5^^ p.m., and the maximum negative about 1'' a.m. ; whence, as in the analogous discussions for 

 the magnetic declination and horizontal component, we may conclude that the smallest and largest disturbances 

 obey the same diurnal law. (See pp. 345 and 368.) 



Differences of the Individual Observations from the Ilontlily Means for the Corresponding Hours. — Adopting 

 the process already indicated for the magnetic declination, p. 346, we obtain the following Table : — 



TABLE L. — Mean Difference of a Single Observation of the Balance Magnetometer from the Monthly 

 Mean, at the corresponding hour, for each Civil Day and Week in 1844. 



Annual Variation of the Mean Difference for the Vertical Component. — The average difference of an 

 observation in each month, from the monthly mean at the corresponding hour, is as follows, in parts of the 

 vertical component. 



Jan. Feb. March. April. May. 



0-000 I 123 157 294 224 203 



These quantities give the same annual law as the similar discussions of the two other elements. The 

 maxunum disturbance of the vertical component occurs near the equinoxes, and the minimum near the solstices. 

 The effect of distm-bance is greatest on the means for this component ; the amount of disturbance of the 

 individual observations (independently of sign), is also much the greatest for the vertical component ; the 

 average difference of a single obsei-vation from the monthly mean for the corresponding hour is fi-om ^- to 4- of 

 the mean diurnal range as deduced from the whole series of observations for each month of the year. 



The mean difference of an observation of the vertical component for the year 1844 = 0-000184. 



MAG. AKD MET. OBS. 1844. 



5 E 



