236 



Results of Monthly Observations of 



[Jan. 27, 



Horizontal Force. 



The monthly values- of the horizontal force, as observed by the Kew 

 Unifilar, are given in Table III. 



The method of reduction is the same as that used in the two former 

 papers, described in the first. 



Table III. 



Monthly Values of the Horizontal Component of the Magnetic Force at 

 Kew, computed from the Experiments of Deflection and Vibration with 

 the Collimator Magnet KC 1. 





1869. 



1870. 



1871. 



1872. 



1873. 



1874. 



Mean of 

 6 years. 



April 



May 



June , 



July 



August . . . 

 September 



3-8499- 



3-8504 

 3-8546 

 3-8562 

 3-8495 

 3-8530 



3-8542 

 3-8502 

 3-8560 

 3-8619 

 3-8660 

 3-8552 



3-8599 

 3-8636 

 [3'8622] 

 3-8608 

 3-8623 

 3-8646 



3-8642 

 3-8723 

 3-8688 

 3-8704 

 3-8701 

 3-8746 



3-8762 

 3-8758 

 3-8773 

 3-8794 



3-8785 

 3-8797 



3-8801 



3-8857 

 3-8816 

 3-8812 

 3-8849 

 3-8768 



3-8641 

 3-8663 

 3-8668 

 3-8683 

 3-8685 

 3-8673 





3-8523 



3-8572 



3-8622 



3-8701 



3-8778 



3-8817 



3-8669 





1869-70. 



1870-71. 



1871-72. 



1872-73. 



1873-74. 



1874-75. 



Mean of 

 6 years. 



October ... 



November 

 December 

 January . . . 



February 

 March . . . 



3-8544 



3-8567 

 3-8473 



3-8576 

 3-8529 



3-8783 



3-8519 

 3-8621 

 3-8575 

 3-8590 

 3-8634 

 3-8642 



3-8700 

 3-8647 



3-8657 

 3-8682 

 3-8594 

 3-8672 



3-8731 



3-8641 



3-8735 

 3-8698 

 3-8747 

 3'8790 



3-8691 



3-8746 

 3-8856 

 3-8768 

 3-8792 

 3-8803 



3-8843 

 3-8815 

 3-8810 

 3-8846 



3-8882 

 3-8833 



3-8671 

 3-8673 

 3-8684 

 3-8693 

 3-8696 

 3-8754 





3-8579 



3-8597 



3-8659 



3-8724 



3-8776 



3-8838 



3-8695 





3-8551 



8-8585 



3-8640 



3-8712 



3-8777 



3-8828 



8-8682 



The number within brackets is interpolated. 



The absolute values of the horizontal force corresponding to tha 

 beginning of October in each of the years from 1869 to 1874 and the 

 secular change in each year are as follows : — 



Table IV. 

 From April 1869 to March 1870 3-8551 



1870 

 1871 



1872 

 1873 



1874 



1871 3-8585 



1872. 3-8640 



1873 3-8712 



1874 3-8777 



1875 3-8828 



Secular change. 



+ •0034 



+ •0055 

 + •0072 

 + •0065 

 + •0051 



Mean of the six years corresponding 'l o.g^^Q Mean secular "i , A,rr 



to the middle epoch, April 1, 1872 J 



change .... J 



