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, 6 represents the 
mean 3 for Jan. 1, 1838, and 4 the annual change’ of dip. 
Observations. eo a. equations of condition. pc. ey ~ 
me Se spt. 8, 72°492 | 0+ .6844=8/2 oe es 
1839. nee 2, 46.8 64-1.3044=6.8 —1.4>.. 
1840. Jn tt 49.5 | 64+2.0274=9.5 | 41.2 
l, 49:5 |°342.665729.5 Lig 
1841. May 10,° °° 47.4 | 94:3.358047 4 —12 
v. 4, 48.7° | 843,.841928.7 0.0 
: These equations give us 0=7’.95, or the mean dip Jan..1, 1838, 
equals 72° 47/.95, 4==+0/’.18, from which we obtain the differ- 
ences between the observed and computed dips as given: in the ' 
last column above. I consider then +0’.18 to be a near er 
mation to the annual change of dip at this place. 
Through the politeness of Lieut. C. W. Younghusband, I hase 
been furnished with a copy of the dip observations made at T'o- 
ronto for 1841. ‘The observations are seventy three in number, 
made generally twice a week, from April 10th to the end pei . 
year. These have furnished me the following equations of con- 
dahamy it ola pees the eerie See, 1, 1841, and 
4 the ; annual motion. ‘ ee 
Ts ~Egnations. - | a tia — 3 
p+ 2a 6 8 
: 2.5 Y — 
"Vol xuint, No. 1-—ApriSune, 1382, 
