TERRESTRIAL MAGNETISM. 



15 



Then: as cos. 11° 9.9919466 



toR 10 



so cot. 72° 01' 33" 9.5111100 



And: as cos. 11° 9.9919466 



toR 10 



so cot 71° 53' 02" 9.5147644 



to cot. 71 42 42 9.5191634 to cot. 71 34 03 9.5228158 



As the above results, from the dip in azimuth, agree very nearly with the dip 

 direct, I have included the last in the calculation, giving a double value to the mean 

 of the readings in azimuth, as follows : — 



71° 34' 03" 

 71 34 03 

 71 37 34 



214 45 40 



Finally, 



71° 



71 



71 



42' 42" 

 42 42 

 40 45 



215 06 07 



71 



42 02 by No. 2. 



By No. 2, 71° 42' 02" 

 By No. 1, 71 35 13 



Mean 71 35 13 by No. 1. 



Mean, 71 38 37 = Dip at Port Norris. 



It will be observed that the letters E.E., E.W., &c., stand for the position of the 

 face of the dip-circle and of the needle ; the first letter indicating the position of 

 the instrument, and the second that of the needle. 



Dip. 



Epoch of 



Duration 





Calculated 



commencing 



of 500 



as 



duration 



vibration. 



vibra- 



at 60°. 



hrs. min. sec. 



tions. 



H S 





Square of the 

 preceding. 



Horizon- 

 tal inten- 

 sity. 



Total in 



tensity : 



hor. being 



1000. 



Total inl 

 sity : that at 

 Cincinnati 

 = 1000. 



172. Bombay Hook Lighthouse.— Lat. 39° 21' 43" N. Long. 75° 33' 22" W. June 17. 

 1846. 



71° 38' 21" 



4 



9 51 00.2 A 



1156.0 



81.25 



1154.42 



13326855364 



924.72 





Var. 3 17 56 W. 



5 



10 20 01.4 



1405.2 



82.00 



1403.00 



19684090000 



923.90 







6 



10 46 44.0 



1400.8 



89.00 



1397.23 



19520116729 

 Mean 



925.79 

 924.80 



2935.87 



984.84 



173. Hawkins, N. J.— Lat. 39° 25' 30" N. Long. 72° 20' 07" W. June 21, 1846. 



71° 43' 41" 

 Var. 2 58 43 W, 



12 55 00.6 P 

 1 24 04.4 

 1 53 20.0 



1153.4 



1400.8 

 1397.2 



82.25 

 86.00 

 86.00 



1151.73 



1398.46 

 1394.00 



13264819929 



19556903716 



19432360000 



Mean 



929.05 

 929.90 

 929.97 

 929.64 



2965.10 



994.65 



REMARKS. 



172. Bombay Hook Lighthouse. — Geology: tertiary of New Jersey. 



173. Hawkins, N. J. — Geology: tertiary. In this neighborhood there is some ferruginous sandstone, 

 but it is hardly magnetic. 



