Vertical Component of Magnetic Force. 



387 



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

 Monthly Mean, at the corresponding hour, for each Hour in each Month of 1844. 



TABLE LIII. — Mean Difference of a Single Observation from the Monthly Mean, at the correspond- 

 ing hour, for each Hour in each of the Astronomical Quarters, and in the Year 1844. 



Diurnal Variation of the Mean Difference. — The mean difference for the vertical component has a well- 

 marked maximum twice, and minimum twice, in the day. In the means for the year, the principal minimum 

 occurs about lO*" a.m., the principal maximum about b^ p.m. ; a secondary minimum occurs about 9^ p.m., and 

 a secondary maximum about 2'' a.m. The values of the maxima differ little from each other, and the principal 



