Dip and Variation of the Magnetic Needle. 108 
southerly —1/.6, at the tem most easterly — 042, atthe ten» mince 
westerly -+.0/.8, at the nineteen intermediate — 0/.3.. ‘ 
‘The preceding comparisons furnish us with the idlicniton re~ 
sults, where column third shows the dip, column fourth the diree- 
tion of the isoclinal line, and column fifth the increase of. dip in 
the normal direction for sixty geographical miles at the points 
whose latitudes and longitudes are shown in the first and et 
columns. eS 
«Latitude. Longitade, | Direction of isoclinal line.” Tne 
“1° 1’ | 73° 52” | 730 62.68 | N. 86° 60’ W. 80-01 sa | 
Al 18 | 81, 12.172 58.11 | N.75 42 W. | 65.081 
40 57 | 84 11°| 72 18.97 |S. 87 8 W. 53 .088 
(42 | 8S 47 | 71° 41.49 | N81 44 W. 58 .106 
With these data, we may trace with some confidence the 
isoclinal lines.of 72° and 73°. “They will pass through the fol- 
lowing points. 
“So Line of 73° dip. . Line of 72° dip. i Zep 
‘gue Latitude, , | Longitude. | ___ Latitude, |_Longitude. — Re 
“20° 47/85 | 73° 52 || 39° 35/85 | 73° 52’ |"N- 86° 50’ W. 
Al 20.12 | 81 12 | 40 12.67 | 81 12 !N.75 42° W.! 
41 43.43° 84-11 | 40 35.54 84> 11 op 8 W. 
42 23.92 |-89 47: |) 41 21.32 | 89. 47 | N. 81°44 W:; 
The isoclinal lines are curved fice passing ‘through the above 
named points sat in 1 the directions eae aiven, Ja the eastern. 
the: 
| and ak, 
ge larity soon. ceases, , 
the neighborhood ve 3 ‘the Pica devcliand lines are tolera- 
bly well represented by portions of the same ¢ircular arcs as near 
the Atlantic. The position here described ‘differs but slightly 
from that represented on my chart, Vol. 39, p. 41. Other isoclinal 
lines may be drawn on each side of these from the same data, but 
With somewhat greater uncertainty. How now are we to regard 
the differences contained 1 in the last column of the preceding ta- 
bles? Do they indicate errors of observation,* errors of the hy- 
oy ar a a id el SS Se 
Mee ps 
edie: aper of 
* Imuch regret that Prof Locke should have interpreted a paper of mine 
Caley n-8) as a ‘special effort to discredit his observations.’ Such was far 
my intentio hed etnags ol Ba Lach’ observations as exceed: 
133. . region hither wholly unex- 
ie a a ee ae ee as ; 
