18 Capt. H. G. Lyons. [June 6, 



Secular Variation of Dip. 



Place. 



Observer. 



Date. 



DiiD. 



Yearly 

 change. 





Quesnot and 



1798 



o , 



47 30 







Nonet. 











p 



1842 



43 48 



-5-0 





Gfiissfeldt. 



1876 



42 52 



-1-6 



,, (Rainleh) 



d'Abbadie. 



1884 



42 47 -7 



-0-7 



Cairo — 











Great Pyramid. . . . 



d'Abbadie. 



1839 



41 41 -8 





>» 



1885 



40 46*8 



-1 -2 





H.G.L. 



1901 



40 31 "6 



-1-0 





d'Abbadie. 



1885 



33 7 7 







H.Gr.L. 



1895 



33 38-1 



+ 3-0 





1 









Secular Variation of Horizontal Force. 



Place. 



Observer. 



Date. 



H. in 

 C.G .S. 

 units. 



Annual 

 change. 







1842-5 



'27955 







Giissfeldt. 



1876 



-2914 



+ -00036 



(Rami eh) 



d'Abbadie. 



1884 



-2971 



+ -00067 



Cairo, Abbassia .... 



d'Abbadie. 



1884 



0-30159 







H.Gr.L. 



1895 



-30076 



-0-00008 





H.Gr.L. 



1896 



-30038 



-o-oooio 



Great Pyramid .... 



d'Abbadie. 



1885 



0-3034 





H.G.L. 



1901 



-2992 



-0 -00026 





d' Abbadie. 



1885 



0-3249 







H.Gr.L. 



1895 



-32070 



-0-00042 





d'Abbadie. 



1885 



-3259 







H.Gr.L. 



1895 



0-32364 



-0-00023 



As the observations for declination given in Tables la, b, c and Ha 

 were all made between the autumn 1893 and the spring 1895, during 

 which time the secular decrease would have been about 5', equal to 

 about half the amount of the diurnal variation, no reduction to an 

 epoch has been attempted. The values obtained by observation have 

 been plotted on the accompanying map, and the isogonic lines drawn 

 between them by hand. 



