in the Diurnal Motion of the Magnetic Needle. 433 



1785. 

 January 

 February 

 March 

 April 

 May 

 June 

 July 

 August 

 September 

 October 

 November 

 December 



1786. 



January 

 February 

 March 

 April 



Magnitude of the 

 diurnal motion. 



Magnitude of th( 

 diurnal motion. 



6-50 



7-19 



9-82 



1099 



1449 



11-75 



11-74 



13-49 



14-35 



12-22 



925 



7-84 



10-27 

 10-68 

 15-41 

 17-06 



1786. 

 May 

 June 

 July 

 August 

 September 

 October 

 November 

 December 



1787. 

 January 

 February 

 March 

 April 

 May 

 June 

 July 

 August 



Magnitude of the 

 diurnal motion. 

 1787. 



14-62 

 14-89 

 15-82 

 15-72 

 15-65 

 16-82 

 10-24 

 10-82 



14-30 

 15-13 

 18-19 

 16-03 

 14-58 

 14-72 

 17-93 

 18-80 



September 

 October 

 November 

 December 



1788. 



January 



February 



March 



April 



May 



June 



July 



August 



September 



October 



November 



December 



15-92 

 13-40 

 12-09 

 1058 



10-20 

 1065 

 16-87 

 20-51 

 16-88 

 15-00 

 12-09 

 11-71 

 13-59 

 12-09 

 11-75 

 10-42 



Calculating from this, in the manner already pursued, the 

 average for the year, and then the mean for the summer and 

 winter half-year, we obtain — 



We here again detect a regular period, with a maximum at 

 about 1786-5. 



Setting the above results together, we find that we are in 

 possession of four series of observations, made at different places 

 and at different times, all of which show a periodical increase 

 and decrease of the diurnal motion of the needle. The maxima 

 full in the following years : — 



1848-5 

 1837-5 

 1817 

 17865 



Permitting the first and last numbers to remain, and assuming 

 Phil. Mag. S. 4. Vol. 3. No. 20. June 1852. 2 F 



