286 



OBSERVATIONS OF THE 



Needle No. 2. 





Date. 



Poles Direct. 



Poles Reversed. 



Dip Deduced. 





Mark East. 



Mark West. 



Mark West. 



Mark East. 



1841, May 18, 7—12, A. M. 



56° 34'.5 



— 42° 49'.9 



63° 



9'.2 



— 52° 36'.0 



72° 43'.4 





( t( <( 



57 31 .7 



— 44 52.4 



61 



30.6 



— 49 22.8 



43.1 





( (1 t( 



53 47.2 



— 38 20.6 



55 



56.2 



— 39 17.3 



52.2 





( (( (& 



47 43.2 



— 27 55.8 



53 



58.5 



— 34 49 .1 



49.6 





1( (( (( 



43 9.5 



— 19 43.4 



44 



12.6 



— 17 29 .4 



48.8 





( (( >( 



40 8.1 



— 14 24.2 



39 



55.2 



— 10 19.0 



43.8 





( (( (b 



36 24.2 



— 8 33 .2 



34 



57.2 



— 3 13.8 



51 .3 





' 1— 4, P. M. 



31 3.1 



— 54.1 



30 



2.3 



+ 3 32.3 



53.4 





1 (i «( 



25 52.7 



+ 6 20.6 



25 



2.0 



+ 9 41 .9 



47.3 





1 (( (( 



22 43 .0 



+ 10 35 .2 



21 



3.3 



+ 13 23.3 



52.5 



<( (( t( (< 



15 36.3 



+ 18 48 .3 



15 



55.2 



+ 18 35 .8 



46.1 



Mean of 1 1 o 



bservations, Neec 



le No. 2, ( 



880 readings,) 



72° 48'. 3 



The discordances between the individual results are somewhat greater than 

 had been expected, nevertheless the average agrees very closely with the dip 

 formerly obtained. This method of observing has the advantage of testing 

 successively every part of the axis of the needle, yet, otherwise, it is much in- 

 ferior to the common method, for the load serves to increase the friction of the 

 axis, and the same error in the observations produces greater influence on the 

 results. In order to determine what correction should be applied to observa- 

 tions made in the usual method, we need first to know the annual chansre of 

 dip. For this purpose I have compared observations made at this place since 

 1838. The following table exhibits the materials for comparison. In the 

 equations of condition, S represents the mean dip for January 1, 1838, and A 

 the annual change of dip. 



Observations. 



Equations of Condition. 



Differences. 



1838, Sept. 8, 72= 



48'. 2 



5 + .684 A = 8'.2 



+ O'.l 



1839, April 22, 



46.8 



S + 1.304 A = 6 .8 



— 1 .4 



Aug. 17, 



48.4 



6 -f 1.624 A = 8.4 



+ 0.2 



1840, Jan. 11, 



49.5 



5 + 2.027 A = 9 .5 



-1- 1.2 



Aug. 31, 



49.5 



S + 2.665 A = 9 .5 



+ 1.1 



1841, May 10, 



47.4 



6 + 3.353 A = 7.4 



— 1 .2 



Nov. 4, 



48.7 



5 -f- 3.841 A = 8 .7 



0.0 



These equations, being solved by the method of minimum squares, give 

 5 = 7'. 95, or the mean dip, January 1, 1838, 72° 47'. 95, A = + 0'.18, from 



