240 Dr. B. Stewart on Observations of Dip [Mar. 3, 



Table VIII. 



Date. 



Observed secular 

 change. 



Observed minus average 

 secular change. 



- 



1857-58 



•0051 



— -0003 



1858-59 



•0057 



4- '0003 



1859-60 



•C056 



-j-*COG2 



1860-61 



•0058 



-[-'0004 



1861-62 



•0044. 



— •0010 



1862-63 



•C051 



— X003 



1863-64 



•co68 



+ •0014. 



1864-65 



•0022 



—•0032 



1865-66 



•0085 



+•0031 



1866-67 



•oc 7 6 



-|-*0022 



1867-68 



•0026 



— -0028 



If we take the first three and the last two of the above differences as 

 belonging to years, when the disturbances are increasing, we find a secular 

 change only less than the average by a mean of '00008 ; and if we take the 

 remaining six differences as belonging to years when disturbances are de- 

 creasing, we find a secular change greater than the average by a mean of 

 •00007; both being differences which form such an extremely small pro- 

 portion of the whole change that they may be neglected. 



18. Or again, if we take the first year's horizontal force (1857) or 

 3*7899, and add to it every year -0054, which is the average secular change, 

 we shall, as before, obtain a series of values representing the yearly positions 

 of the line A E D in the diagram, from which we may construct the follow- 

 ing Table similar to Table IV. 



Table IX. 



Observed yearly 

 values. 



Yearly values of 

 AED. 





(1) 



(?) 



(l)-(2) 



3-7899 



37899 



o-oooo 



3795° 



37953 



— 0*0003 



3-8007 



3-8007 



o-oooo 



3-8063 



3-8061 



+ 0-0002 



3-8121 



3-8115 



-j-o'ooo6 



3-8165 



3-8169 



— 0-0004 



3-8216 



3-8223 



— o-coc7 



3-8284 



3-8277 



4-0-0007 



3-8306 



3-8331 



— 0-0025 



3'S39 T 



3-83^5 



4/-o-coo6 



3-8467 



38439 



+ 0.0028 



3-8493 



3-8493 



O'COOO 



From this Table we fail to perceive a trace of the behaviour exhibited by 

 the dip in Table IV. 



Apart, therefore, from all theoretical considerations, we have reason to 

 believe that, as a matter of fact, the behaviour exhibited in the diagram 

 holds for the dip, but does not appreciably manifest itself in the case of 

 the horizontal force. 



