DISCUSSION 



SOLAR DIURNAL VARIATION, AND OP THE ANNUAL INEQUALITY OP THE VERTICAL 

 COMPONENT OF THE MAGNETIC FORCE AT PHILADELPHIA. 



THE necessary data for this investigation are given in the preceding Part (VII), 

 which contains the normals resulting from the reduction of the observations to the 

 same temperature (66 Fah.), from the allowance for irregularity in the progressive 

 change and the exclusion of all recognized disturbances. 



Owing to the greater irregularity in the indications of the vertical force instru- 

 ment, and the comparatively small number of observations at odd hours, the normals 

 are given for the even hours only ; the observations at odd hours, however, are used 

 to improve those taken at the intermediate even hours by means of a suitable pro- 

 cess of interpolation. 



The tabular numbers are expressed in scale divisions, one division being equal 

 to 0.000033 parts of the vertical force, or equal to 0.000423 in absolute measure. 

 Increasing numbers denote decrease of force. The hours count from midnight to 

 midnight to 24 hours ; the number of minutes the observations are made later than 

 the full hour are given in the last column for each month. 



1 Let reading for any even hour = n for the year 1844, for the odd hours preceding and following n p & nf, mean 



np-\-nf np+ny 



2 ~; hence mean for the even hour J (n + -- <j - ) which was substituted before the general mean for the 



four years was taken. 



( 37 ) 



