INVESTIGATION 



OP THE 



INFLUENCE OP THE MOON ON THE MAGNETIC VERTICAL FORCE. 



THE method of discussion of the lunar effect on the vertical component of the 

 magnetic force in no way differs from that employed for the horizontal component, 

 which latter has been explained in Part VI. 



The series of observations available for the lunar discussion extends from Febru- 

 ary, 1841, to June, 1845, inclusive. From February, 1841, to October, 1843, the 

 observations are bi-hourly ; from October, 1843, to the end of the series they are 

 hourly. The record of May, 1841, is not quite complete, and in January, February, 

 ami March, 1843, but one observation a day is recorded. As increasing numbers 

 demote a decrease of force, a positive sign of the tabulated differences between 

 monthly normals and each individual undisturbed reading (at the normal tempera- 

 ture) indicates a greater force than the normal value, a negative sign indicates the 

 reverse. 30 scale divisions being the limit beyond which difference an observation 

 has been considered as belonging to the class of disturbances, all differences here 

 recorded are below this limit. One scale division is 0.000033 parts of the force. 

 The tabular numbers are expressed in scale divisions. 



In tracing out the lunar effect upon the vertical force we have to contend with 

 greater irregularities than was experienced in the case of the horizontal force. The 

 vertical force magnetometer is more subject to changes, and the correction for tem- 

 perature far exceeds that of the horizontal force. 



The total number of observations and differences formed in the inquiry of the 

 dependence of the force upon the moon's hour angle is 19513, which distribute 

 themselves over the months and years as follows : 



