Dip and Variation of the Magnetic Needle. 



97 



The observations made at Hudson are confined to a short pe- 

 riod, nevertheless they possess certain important advantages for 

 comparison. They were all made with the same instrument, at 

 identically the same locality, by the same individual, and after 

 the same method. The following table exhibits the materials 

 for comparison. In the equations of condition, <^ represents the 

 mean dip for Jan. 1, 1838, and ^ the annual change of dip. 



These equations give us <5=:7'.95, or the mean dip Jan. 1, 1838, 

 equals 72° 47'.95, z?— + 0M8, from which we obtain the differ- 

 ences between the observed and computed dips as given in the 

 last column above. 1 consider then +0M8 to be a near approxi- 

 mation to the annual change of dip at this place. 



Through the politeness of Lieut. C. W. Younghusband, I have 

 been furnished with a copy of the dip observations made at To- 

 ronto for 1841. The observations are seventy three in number, 

 made generally twice a week, from April 10th to the end of the 

 year. These have furnished me the following equations of con- 

 dition, in which 8 represents the mean dip for Jan. 1, 1841, and 

 J the annual motion. 



Equations 



(J-|-.271^: 



(5+.282z/z 



(J-f.290^; 

 J_[-.301z/: 



,y_[_.309^: 

 ^-j-.320^z 



<5-f.339^= 

 <5-|-.348^z 

 <J4--359^r 

 <>-|-.367^z 



<^-|--386^: 

 '^-{-.397^1 



6.8-fl.7 

 4.2-1.0 



6.1 

 5 



8.4 



-fO.9 

 



:-f3.1 



: 6.2'4-0.8f 



: 7.l|4-l.'3' 



1 5.6+0.1 

 : 4.9-0.7 

 : 5.3-0.3 

 : 7.3-1-1.6 

 :13.3'4-7.6 

 : 9.7:-|-3.9 

 : 2.5-3.3 



Equations. 



(5-j-.405^: 



8-\-A\Gjz 

 8-\-A24.jz 

 (5-j-.435z?= 

 (J-|-.444^z 

 d-\-A54dz 

 8j^A63Jz 

 (J_|_.474^z 

 8j^A82Jz 

 8^Ad3zlz 

 <^-^.520^z 

 '^-^.531^z 

 '^-|-.539^z 

 '^-i-.550^z 



3.0 -2.9 

 3.6 -2.3 



6.2|-f0.2 

 ■ 0.9 



5.2! 



: 6.2'-f0.1 



: 8.3 4-2.1 



: 8.4'-J-2.2 



: 6.5U-O.2 



: 5.0-1.3 

 :11.9-f5.5 



: 9.24-2.7 



: 4.8 



: 3.6 



: 1.6 



-1. 



-3.0 

 -4.9 



Equations. 



(J+.559^z 

 (5-i-.569^z 

 8-]-.518^z 

 8-^.589^z 

 (y-f-.597.4z 

 8-\-.608^z 

 8-\-.6l6dz 

 8-\-.62lJz 

 (5-j-.635^z 

 8-{-M6Jz 

 8-{-.654^z 

 'J-|-.665^z 

 <y-f-.674^z 

 'y-f.684^z 



: 3.4 



: 3.3 



: 5.6 



: 4.0 



: 5.4 



: 2.5 



: 4.7 



: 3.3 



: 3.0 



: 6.3 



: 2.4 

 :10.6 



: 9.2 



: 1.5 



Diff. 



-3.4 

 -3.5 

 -1.3 

 -2.9 

 -1.6 

 -4.5 

 -2.4 

 -3.8 

 -4.2 

 -1.0 

 -4.9 

 +3.2 

 + 1.8 

 -6.0 



Vol. XLiii, No. 1.— April-June, 1842. 



13 



