TERRESTRIAL MAGNETISM. 



17 



Dip. 



Epoch of 

 commencing 

 vibration, 

 hrs. min. sec. 



Duratior 

 of 500 

 vibra- 

 tions. 



Calculated 

 duration 

 at 60°. 



Square of the 

 preceding. 



Horizon- 

 tal inten- 

 sity. 



tensity : 

 hor. be- 

 ing 1000. 



Total inten 



sity : that at 



Cincinnati 



= 1000. 



179. Pilottown, Del.— Lat. 38° 47' 04" N. Long. 75° 12' 15" W. July 3, 1846. 



71° 16' 16" 

 Var. 2 41 56 



2 23 59.8 P 

 2 50 00.2 

 12 13 52.0 



1144.0 

 1390.0 



1384.8 



82 5 



78.0 

 78.0 



1142.33 



1388.25 

 1382.61 



13049178289 



19272380625 



19115827600 



Mean 



943.94 

 943.64 

 945.38 

 944.19 |3140.59 



986.42 



180. Chew, N. J.'— Lat. 39° 49' 21"? N. Long. 75° 12' 57"? W. July 15, 1846. 



72° 14' 37" 

 Var. 3 20 22 



11 03 35.6 A 

 11 23 37.2 

 1 57 02.8 P 



1169.2 

 1420.8 

 1416.0 



80.0 

 79.5 

 75.4 



1167.68 

 1419.00 

 1414.08 



13632565824 



20135610000 



19996222464 



Mean 



903.98 

 903.18 

 903.75 

 903.64 



2962.70 



993.86 



181. Vanuxem.— Lat. 40° 05' 46"? N. Long. 74° 47' 00"? W. July 10, 1846. 



72° 21' 29" 

 Var. 4 20 32 W. 



L 



8 20 00.8 A 



8 57 1.2 



9 55 01.2 



1176.4 



90.0 



1174.10 



1429.2 



91.5 



1426.05 



1424.4 



93.5 



1420.20 



13785108100 893.97 



20336186025:894.27 



201696804001895.98 



Mean 1894.74 



2952.32 



990.36- 



REMARKS. 



179. Pilottown, Del. — Geology: tertiary. On an arable bank of an inlet. 



180. Chew, N. J. — Locality: a hill, but, so far as could be seen, without hard rocks. Geology: ter- 

 tiary. I conceive this to be a more unexceptionable locality than Girard College, and as it is south of it, 

 and still exhibits a higher dip, I infer that the dip at that station is made by some local attraction too low 

 for its geographic situation. 



181. Vanuxem. — Locality: at Prof. Vanuxem's, about two miles above Bristol, Pa., and near the 

 canal. Geology: diluvium of clay, sand, and gravel, superimposed on primitive rocks? At a distance of 

 a mile or more to the north-west, a heavy dike or ridge of trap-rock crops out along the surface. 



X. Series for 1847. 



Ever since my journey to Lake Superior in 1844, I had been extremely desirous 

 to make a further exploration of the extraordinary magnetism which I found to 

 exist there. An appropriation for a geological survey of that region, in 1847, 

 afforded the opportunity of attaching magnetical observations to those more spe- 

 cifically geological. Such, however, is the connection of the two subjects, and espe- 

 cially in that region, that the one is incomplete without the other. At the request 



' The name of a coast survey station, derived, as many such names have been, from the name of some 

 neighboring resident. 



" This result disagrees with that obtained at Prof. Vanuxem's in 1842 (985); but it should be observed 

 that the stations were not identical, this station (1846) being several hundred feet to the westward of the 

 former. So near as I found we were to trappean rocks, it is not strange that so much difference should 

 exist. 



5 



