- Dip and Variation of the Magnetic Needle. 115 
Central position, latitude 46° 41’ N., longitude 87° 6 W., d= 
4°.00489, i. e. —4° 0.3, x= —.003988, y= +.024886. Mean 
of the differences at the six most northern stations —1/.8; five 
southern +2’.2; three most easterly +3/’.0, three most westerly 
-+3/.3; five intermediate —3’.8. : : . 
Collecting together the preceding results, we obtain the fol- 
lowing table, in which column third represents the variation for 
places whose latitude and longitude are given in columis first 
and second; column fourth, shews the direction of the lines of 
equal variation ; column fifth, the increase of variation in the nor- 
mal direction for sixty geographical miles; and column sixth, the 
distance of the lines of equal variation expressed in geographical 
miles. 
[_tatitide. ~]_Longitade. Variation. Direction of lines.| Increase. |Distance of lines. 
44°55’ n. 69°31 w.|/+ 13°137.9\n. 50°40 
43 24 |72 57 |+ 8 26.9. 39 13 w 
42. 5 75.12. |+ 6. 5.0nN. 26 36 .w 
43 49 (84 4 |— 2 20.6n. 10 59 w 
40.53 (81 2° |— 0 36.2in. 22 19 w 
39 52. + |83 40 3.30 ,8in. 11 24. w 
32 46 (81 55. |— 4 47.4. 20.17 w 
32.48 (84 19 (6 On. 7 Ai w 
32.6 (91 8. |— 7 67.5. 8 
39 12 (89 22 j— 7 35.1\N. 6 
42 28 (90 25. |— 8 48.3\n. 13 a 
46 41 (87 6 |—4 0.3m 9 68°) 
From these data are computed the win, 
lines of equal variation, = mage Os, 
13. |44 45..9/69. 31 n.50 7 w. sf wats D 6 es. 
9 |43 24 |72 18.0) n.41 17 w. (ee wn. 9 20 w. 
43 24 3 28 | N..37 32 Ww. 4 w. 20°17 w. 
{ 42.5 n.27 17 w. 5. BN. 2 26 w. 
+ 42 5 |75 18.0) x. 26 32 w. 8 ‘NW. ‘8 57 w. 
» 143 49 183 44 4] v.12 16 w. : ee Ni 3°24R) 
43 49 |84-41.5) m 8 31 w. 8 Nn. 7.39 kz. 
} 140 53 180 13.5) nN. 24 35 w. 8 w.1016 £. 
40 53. 181 33.8} wn. 20 50 w. MJ Ww. 14) 1g, 
The preceding positions are each determined from a single group 
of observations, independently of all the others. In projecting the 
lines upon a map, some anomalies will be perceived as to the di- 
‘rection of the lines and their distance from each other. The righ 
emarkable of these is the line —4° in latitude. 32° 46% The - 
mo 
