12 



OBSERVATIONS ON 



Dip. 



Epoch of 

 commencing 

 vibration, 

 hrs. min. sec. 



Duration 





Calculated 



of 500 



11 



duration 



vibra- 



at 60°. 



tions. 



E-1 ^ 





Square of the 



Horizon- T otal in- 

 tal inten- tensity : 

 sity. hor. be- 

 ing 3000. 



Total inten- 

 sity : that at 

 Cincinnati 

 = 1000. 



164. White Hill, Woodland Station, about half a mile east of the Survey Station.^ — Lat. 40° 08' 

 17"? N. Long. 74° 46' 46" ? W. May 21, 1846. 



72° or 23" 



4 

 5 

 6 



8 12 01.2 A 



8 43 00.8 



9 14 01.2 



1163.2 

 1415.2 

 1410.4 



66.0 

 65.5 

 67.0 



1162.82 

 1414.80 

 1409.55 



13521503524 



20016590400 



19868311025 



Mean 



911.41 



908.55 

 909.57 

 909.84 



2947.4 



988.61 



165. Girard CoUege, Philad.— Lat. 89° 58' 21" N. Long. 75° 12' 57" "W. May 23, 1846. 



72° 00' 58" 

 Var. 3 50 44 W. 



9 02 03.0 A 

 9 34 32.0 

 10 13 02.8 



1163.6 

 1414.4 

 1408.4 



79.5 

 84.0 

 78.0 



1162.13 

 1412.66 

 1406.63 



13505461369 



19956082756 



19785079569 



Mean 



912.49 

 911.31 

 913.30 

 912.37 



2955.1 



991.31 



166. Wilmington.— Lat. 39° 44' 53" N. Long. 75° 36' 39" W. May 29, 1846. 



71° 24' 39" 

 Var. 2 31 46 W. 



8 06 01.6 A 



1149.8 



61.0 



1149.73 



2 02 59.6 P 



1396.8 



68.0 



1396.02 



2 38 04.0 



1392.4 



68.5 



1391.36 



13202010000 



19488718404 



19358826496 



Mean 



933.47 

 933.16 

 933.51 

 933.38 



2931.85 



983.50 



167. Smith's Quarry, near Wilmington.— May 31, 1846. 



74° 11' 41" ! 4 1 49 03.2 1246.8 81.5 1246.00 15500250000 795.06 2912.3 976.95 



REMAKKS. 



164. White Hill, Woodland Station. — Geology : same as above. Day exceedingly clear, calm, and 

 fine. The mean of these two observations corresponds very well with surrounding observations, as foUows : — 



Dip, 72° 03' 48". 



Horizontal intensity, 912.25. 

 Total intensity, 993.51. 



165. Girard College, Philad. — At the usual locality in the yard of the Magnetical Observatory. It 

 will be seen that the total intensity above is less than I have formerly made it to be at this station. I 

 know of no circumstance which will account for this. I bring the various observations at this locality 

 together that they may be compared at one view. 



March' 30, 1841. Total intensity at Girard College, 994.78 



March 31, 1841. " " 994.97 



April 21, 1841. " " 993.24 



May 15, 1842. " " 995.48 



April 19,1844. " " 991.84 



May 23, 1846. " " 921.31 



Mean, 993.60 



166. Wilmington. — Geology : a hill of trap, but the rock does not show itself at the surface, being 

 covered with red clay. Dip and intensity evidently too low for the latitude. 



167. Smith's Quarry. — Geology : the rock at this place is a solid mass of lienitic trap in place. It 

 has a fine prismatic structure, which lies horizontally, in the direction of the meridian; and in this direc- 

 tion it possesses permanent polarity, which it retains after being quarried — even in small hand specimens. 



