DISCUSSION 



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

 COMPONENT OP THE MAGNETIC FORCE AT PHILADELPHIA. 



The necessary data for this investigation are given in the preceding JPart (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 aU 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. 



Normals of the Vertical Force for July. 



Year. 



0" 



1 



2 



3 



4 



5 



6 



7 



8 



9 



10 



ll" 

 780 



1841 

 1842 

 1843 

 1844 



703 

 683 

 691 

 816 



811 



697 

 672 

 692 

 804 



8(16 



687 

 664 

 692 

 805 



802 



671 

 659 

 686 

 798 



793 



667 

 657 

 679 

 784 



783 



664 

 650 

 672 

 782 



Means ' 



722 





717 





712 





703 





698 





692 





1 



Noon 



13 



14 



15 



16 



17 



18 



19 



20 



21 



22 



23" 



Min. 



665 

 643 

 662 

 780 



776 



676 

 643 

 658 

 773 



781 



680 

 647 

 659 

 783 



791 



698 

 663 

 666 

 799 



805 



708 

 677 

 677 

 808 



809 



706 

 682 

 685 

 811 



SIG 



+17 

 +173- 

 +23| 

 +23^ 



687 





688 





693 





706 





717 



721 





+20.4 



' Let reading for any even hour = n for the year 1844, for the odd hours preceding and following np knf, mean 

 np-^-nf np-{-nf 

 2 — '"> lience mean for the even hour J (n + ^ ) which was substituted before the general mean for the 



four years was taken. 



( 37 ) 



