20 OBSERVATIONS ON I. 



would best represent the magnetic quantities ascertained by experiment. No 

 person, within my linowledge, is better qualified for this task than Col. Sabine. I 

 merely wish a comparison of the magnetism of the region south of Lake Superior 

 with that north of it, in order to show that, in the actual state of knowledge in 

 1844, I committed no absurdity in announcing that I had reached what was pro- 

 bably the i^oint of maximum intensity at Lake Superior. The observations on 

 trappean rocks are always irregular, so much so that one does not feel satisfied with 

 a mean of a multitude of observations. I have taken, therefore, only those obser- 

 vations which were made on horizontally-stratified rocks of the aqueous formation. 

 I refer esj)ecially to the observations made along the south shore of Lake Superior 

 from Chocolate River to Little Taquammanon River. These I have compared with 

 the observations made by Capt. Lefroy from Lake Superior to Hudson's Bay. This 

 series of observations was made along a line nearly semicircular in form, beginning, 

 say, at Fort William, Lake Superior, curving westward, and terminating at Hudson's 

 Bay. This curved line passes around Col. Sabine's point of maximum intensity, in 

 general as a centre, and about three or four degrees from that point. It embraces 

 about thirty-two stations, the intensities of which I have grouped into parcels of 

 about four, obtaining the mean in each case as below : — 



Intensity at Capt. Lefrot's Stations North oe Lake Supemoii, proceeding towards 



Hudson's Bay. 



1. Near Lake Superior 1.876 



2. The mean of 4 next in order ....... 1.861 



3. « 4 " 1.859 



4. « 4 « 1.860 



5. " 4 « I860 



6. « 4 U Jggg 



r. " 4 " 1.867 



8. " 5 " 1.869 



9. « 4 « 1872 



Mean = 1.875 



The second and the ninth groups are near the isodynamic line of 1.875 of Col. 

 Sabine. The other intermediate groups are about half way between that of 1.850 

 and 1.875, and their mean is very nearly 1.862. 



Intensity at Stations of Dr. Locke's Survey on the South Shore op Lake Superior, where 

 the Geology is Aqueous and Non-Magnetic. 



Lat. N. Long. W. 



Train River 46° 30' 87° 01' 1.870 



Grand Island . . . . 46 27 86 45 1.875 



Chapel River, Pictured Rocks . 46 43 86 40 1.883 



Portal Rock, " . . . 46 43 86 39 45" 1.883 



Grand Marais . . . . 46 42 86 09 1.872 



Two Heart River . . . . 46 43 85 38 1.868 



Near White Fish Point ... 46 46 85 13 1.888 



Little Taquammanon River . . 46 41 85 13 1.877 



Mean, 1.877 

 Mean of Capt. Lefroy's stations, as above .... 1.875 



Col. Sabine's calculated maximum ...... 1.878 



