SOLAR-DIURNAL VARIATION OF THE DIP AND TOTAL FORCE. 



To make the combination of the horizontal and vertical force components com- 

 plete, there remains the discussion of the regular solar-diurnal variation and its 

 annual inequality, of the resulting dip and total force. 



Table III, of Part V, contains the solar-diurnal variation, expressed in parts of the 

 force, of the horizontal component, freed from the larger disturbances ; Table III, 

 of Part VIII, contains similar information with regard to the vertical component. 

 The numbers of these tables, however, cannot be combined directly, owing to the 

 eleven year inequality which requires that the two sets of components should cover 

 precisely the same interval of time. In the present case the table of the horizontal 

 force extends from July, 1840, to July, 1845, a five year series; whereas the table 

 of the vertical force extends over four years only ; a new table of monthly normals 

 of the horizontal component was therefore prepared, in which the first year's obser- 

 vations were omitted. This was done by the same method as had been followed in 

 the preparation of the former annual values of Part V. The following table differs 

 from that of Table I, of Part V, only in the number of observations employed, and 

 extends from July, 1841, to July, 1845. 



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