80 SEVENTH REPORT—1837. 
9. The highest intensity already observed is more than twice 
as great as the lowest. 
The intensities observed at New York and Hobart Town, 
compared with that at St. Helena, are as 1°81 to 0°84, or as 
2°16 to 1. 
St. Helena is not the lowest intensity; and the force at 
New York and Hobart Town cannot be viewed as abso- 
tensity, appear to have been subject to a considerable instrumental uncertainty ; 
and the needle lost magnetism during the absence from England to a large 
amount, but at what time the loss took place is not very obvious from the ob- if 
servations. Under these circumstances I have not felt that I could assign with y 
sufficient confidence the value of the intensity relatively to Europe at any of ! 
Capt. Back’s American stations. By grouping them, however, and comparing 4 
the values of the intensity in different groups, relatively to each other only, and 
not relatively to Europe, we may considerably lessen the effect of the irregu- 
larities above mentioned, and obtain an indication, which, if we could view it as 
sufficiently clear from instrumental uncertainty, would possess much interest. 
For example, if we group neighbouring stations as in the subjoined table, and 
make the intensity at New York the unity of the comparison, we have as fol- ‘ 
lows: viz. 
r= Mean 
Station. Date| < Lat. | Long. |Time off 3 |——_—__~________ ||. Tntemm 
a T if . 
North West Vib, | & Lat. | Long. va Ther. 
1833] 4, ae s. . uy = S. 3 | 
New York........++ Apr.| 40 42 7401 |1:2857|/69: | 4042] 7401] 1:2857 | 69 || 1-000 
Fort Alexander ...|Jun.} 5037 96 21 | 1-2482| 70-5 a 
Cumberland House |July| 5358] 10222 | 1:2643/59-5 | 5320/10213| 1:2681 | 68 || 1-027 
Isle 4 la Crosse ...... July} 5525] 10755 | 1-2969| 73:5 (a) 
Fort Chipewyan ...|July| 5842] 11119 | 1-3000) 95- j og 
Fort Resolution .../Aug.| 6110] 11345 |1-2387| 65-6 ¢ °956)11232) 12693 ) 80 | 1-035 
Oct.| 6246] 10901 | 1-2750) 44- (0) 
i 1834 
Fort Reliance «+4 (nray| is4:{  vssses [12844149 ( 6246{10901] 1-2792 | 40 || 0-9 
Get.) Sake. |) Near 1-2781| 28- 
Musk Ox Rapid .../July| 6441] 10808 | 1-2873| 64- ‘ 
Rock Rapid ......... July} 6554} 9810 | 1-2800) 87- % 
Point Beaufort...... July| 67 41 95 02 | 1:2975| 72- 6651] 9819} 1-2838 | 70 || 1-002 
Montreal Island ...|Aug.| 67 47 9518 | 1:2885] 74: (cm 
Point Ogle ......... Aug.| 6814] 9458 | 12656] 53- Fi 
Here we see that the groups (a) and (4), which have their mean position about 
53° N. and 102° W., (258 east), and GO N., and 1123 W. (2473 east), have a 
higher intensity than the more northern group (c), which has its mean position 
about 67° N. and 98° W. (262 east). These groups (a) and (6) have alsoa 
higher intensity than that of Fort Reliance to the north, or New York to the 
south. New York, Fort Reliance, and the northern group (c), scarcely differ in 
the values of their respective intensities, This arrangement is quite conformable 
with the lines in the polar map. 
I have taken Capt. Back’s observations from Mr. Christie’s paper in the Phil. 
Trans. for 1836; the times of vibration at the stations in America being those 
contained in the table page 393, That table shows that the needle was vibrated at 
