304 OBSERVATIONS ON THE MAGNETIC DIP, 
The above being a comparison of the results obtained at the above date with those of 
| May 8, 1841, assumed as unity, or, rather, as 1000, exhibit very favourably the perma- 
nency of the magnetism of the needles; and show it to be quite immaterial which, here- 
after, be made the standard of comparison—the observations of May 8, 1841, or those of 
| August 21, 1843. The following calculations will be made by using the above squares 
i as dividends, and will, therefore, refer to Cincinnati, August 21, 1843, as unity. The 
observations were made at the usual locality, in Longworth’s garden. Weather clear 
and calm. 
64. Huron, Ohio, Latitude 41° 21’, N.; Longitude 82° 27’, W.; June 6, 1843. 
release lu. Sige: (Obes EeroMwemedion lc) loometina sit ta ‘Total intensity, 
Dip. No. of | Epoch of commencing | of 500 Tempe-| duration Square of the | Horizontal] Total intensity, that at Cincin- 
Needle. Vibrations. Malate rature, at 60°, Preceding. intensity. | Hor. being 1000, |nati being 1000, 
73°00'00" 4 | 9h.41m.02s.4 A}1180.0 | 63°5/1179.41|1391007.9481'884.99 | 
| 5 10 28 04 0 {1440.0 | 66 5)1439.11]2071087.5921 881.50 | 
i E 11 16 04 0 |1432.8 | 69 5)1431.36/2048791.4496'883.69 
i Mean,'883.40 | 3021.50 | 1012.32 
_ Locality, the low peninsula on the east side of the mouth of the Huron river. The 
immediate soil is diluvium, but, at no great depth, the “black shale” must exist. 
65. Detroit, (Michigan,) Latitude 42° 25’, N.; Longitude 82° 56’, W. 
4 | 8h.21m.02s.4 A/1200, |66°5 
5 |8 48 03 2 |1462. |68 0 
6 | 9 22 O1 2 1456.4 |72 0 
“98° 32" 1199.3 |1438320.4900 ee | 
1460.94 2134345,6836|855.36 
bea 2115948,4369|855.64 
Mean,|855.63 | 3018.55 1011.34 
Near the Pontiac rail-road, about one-fourth of a mile north of the bend. Ancient lake 
bed, similar toa diluvium. Surface level and wet. Substratum, at, perhaps, one hun- 
dred feet below the surface, the cliff limestone. Clear, fine, wind south-west. 
66. Ann Arbor, (Michigan,) Latitude 42° 16', N.; Longitude 83° 39’, W.; June 13, 1843. 
1402140.1744 
°73°12'36"| 4 | 61.29m.02s.0 Pji1185.2 | 71°5|1184.12 877,96 
5 ls 59 O1 2 {1443.6 | 68 0|1442.56/2080979.3536] 877.77 
Mean,! 877.86 3039.00 1018.20 
In the woods south-east of the university. Geology, diluvium of large bowlders. On 
the supposition of equal intensities at Ann Arbor and at Detroit, the calculated dip at 
the former place would be 73° 07’ 30”, 5’ 06” less than the observed dip. 
67. Ann Arbor, June 14, 1843, 
73°14'46"| 6 | 6h.07m.59s.2 A|1437.2 | 57° 5|1437.28]2065773.7984| 876.43 | 3040.40 | 1018.64 
About three hundred feet east of the previous locality. 
68. Detroit, Chancellor Farnsworth’s Garden, June 15, 1843. 
-73°32'25"| 4 | 3h.05m.00s.5 P|1200.2 | 67° [1199.45/1438680.30251855.67 
| 5 |3 36 04 0 |1462.8 | 66 |1462.00/2137444.00001854.11 
Mean,|854.89 | 3017.17 1010.90 
Geology, deep lacustrine deposite, underlaid by the cliff limestone, Cloudy, and a 
slight, misty rain towards the end of the time. 
