300 OBSERVATIONS ON THE MAGNETIC DIP, 
with sandstone in place, but with trap-rocks near. The above experiments were made 
on the eighteenth and nineteenth, and both the dip and horizontal intensity varied con- 
siderably. The last, as indicated by Nos. 4, 5, and 6, on the eighteenth, would be 
879.00; and, by Nos. 1, 2, and 3, on the nineteenth, would be 876.23; a difference which 
| corresponds to a change of dip equal to 3’37”. 'The dip observed on the eighteenth was 
72° 52’, and that on the nineteenth, 72° 46’ which is a range of difference greater than 
that indicated by horizontal intensity, by 2’ 23”. It will be seen that I have taken the 
mean both of dip and intensity; but, by this note, I have put the reader in possession of 
all the facts. Still, 1 am not satisfied with the results at this locality. Will the station- 
ary observers refer to their records for this time? 
47. New York, Columbia College, April 19, 1841; Latitude 40° 43’, N.; Longitude 74° O01’, W. 
Duration | | Calculated ; | Total intensity, — 
Dip. No. of of 500 |'Tempe-| duration Square of the | Horizontal} Total intensity, |that at Cincin- 
Needle Vibrations. Vibrations.) rature. at 60°, Preceding. | intensity. | Hor. being 1000, |nati being 1000. 
: | | 
72° 41’ | 1 4h.19m.59s,6 P}1643.2 | 55° |1644,18)/2703327.8724/876.83 
2 4 55 00 4 {1614.4 | 54 |1615.8 |2610809.64 1884.57 
3 5 27 04 8 {1315.2 | 55 |1315.58)1730750.7364/882.47 
Mean,|883.52 | 2969.20 | 994.282 
Locality, the yard of the college, near the usual place of observation, which was 
pointed out to me by Professor Renwick. But, an iron fence having been erected on 
the outer side of the yard, it became necessary to remove to a place about central between 
that fence and the college building. Geology, deep diluvium, underlaid by gneiss rocks? 
48, Near Harlaem, cight miles north-east of New York, April 20, 1841. 
72°21" [| 1 {ilh.44n.04s. A]1622.4 | 58° 1]1622.65/2632993.0225/900.26] 2969.18 | 994.239. 
Locality, about three hundred feet south-west of the new asylum for the insane, situ- 
ated about one mile from Harlaem. Geology, gneiss rock, covered with soil, and an 
abundance of trappean bowlders, of large size. The dip was so extraordinary that, after 
vibrating one needle, I removed less than a mile, to the old asylum. 
49. Old Asylum, near Harlaem, April 20, 1841. 
2h.09m.028.8* [1635.2 57° 2/1635.78/2675776.2084|885,86 
3 Ol: 00 1618.4 | 54 |1619.81)2623784,4361/880.20 | 
2 48 03 6 (1317.6 | 56 |1317.09/1736860.41 |879.37 | 
3. 20 59 2 (1175.6 56 /1175.9 |1882740.81 (891.47 
4 
4 
72°39'36" 
I 
2 
3 
4 
ne 
9) 
6 
21, 69».6 1439.2 54 1439.8 |2073024.04 |879.83 
50 00 8 (1434, 54, 52 6/1485.4'7|/2060574,1209/880.33 
Mean,|882.84 2961.90 991.800 
Locality, in a grove north-east of the old asylum. Geology, as above. Cloudy, wind 
south-east, sun-veiled, occasionally a little mist of fine rain. 
50. Baltimore, Howard’s Woods, April 28, 1841; Latitude 39° 17’, N.; Longitude 76° 87’, W. 
71°34’ we 1 | 8h.18m,02s. (1589.2 54° 1590.84 /2529181.3156 937.20 
2 8 58 04 1569.6 | 54 1570.95 2467883 .9025/935.80 
é 10 05 03 6. |1276.8 | 57 51277. 1630729. 936.60 
| 4 10 40 00 8 {1146.8 | 65 5 1146.64)1314783.2896)937.55 
5 |11 07 57 6 {1896.8 | 65 {1396.3 |1949653.69 |935.50 
6 H1 42 01 6 {1890.4 | 64 931182.7089)939.31 
_Mean,! 936. 98) 2963. 53 993, 48 
= act time, New York Sd ‘On dhe supposition that the total intensity is the same at both the Seire 
localities, the horizontal intensity would indicate a difference of dip still greater than here exhibited, Making 
72° 21’ the standard, the other would, by such calculation, be 72° 42’ 9”, instead of 72° 89’ 36”. 
