AT SEVERAL PARTS IN THE UNITED STATES. 



65 





Time. 



Horizontal 

 intensity. 



Mean. 



Dip. 



Total 

 intensity. 



'ii.rai 

 intensity. 



New York, 



Hansteen 



867^51 



.96105 



.96707 



72° 52'.2 



1.00815 



1.803 



n 



Sabine 



737 .96 



.96998 











a 



Henry 



593 .81 



.97018 











New Haven, 



Hansteen 



884 .27 



.92497 



.92364 



73 26.7 



.99533 



1.7800 



(( 



Sabine 



756 .40 



.92326 











(t 



Henry 



608 .90 



,92269 











Dorchester, 



Hansteen 



904 .35 



.88435 



.88182 



74 16.0 



.99854 



1.7858 



t( 



Sabine 773 .45 



.88301 











a 



Henry 



624 .17 



.87810 











Providence, 



Hansteen 



897 .46 



.89798 



.89830 



73 59.6 



1.00027 



1.7889 



a 



Sabine 



766 .70 



.89862 











Princeton, 



Hansteen 



862 .29 



.97273 



.97414 



72 47.1 



1.01066 



1.8075 



(( 



Sabine 



734 .22 



.97989 











(< 



Henry 



593 .93 



.96979 











Philadelphia, 



Hansteen 



850 .45 



1.00000 



1.00000 



72 7.1 



1.00000 



1.7884 



(( 



Sabine 



726 .80 



1.00000 











(t 



Henry 



584 .89 



1.00000 











Hudson, 



Hansteen 



860 .74 



.97623 



.97344 



72 47.6 



1.01040 



1.8070 



(( 



Sabine 



737.11 



.97222 



' ' 









(( 



Henry 



593 .29 



.97188 











From the preceding observations it may be inferred that New York and 

 Hudson have sensibly the same magnetic intensity, as well as dip. 



The only published observations, so far as I am aware, with which the pre- 

 ceding can be compared, are those made by President Bache and Professor 

 Courtenay, and published in the Society's Transactions, Vol. VI., pp. 427 — 457. 

 The horizontal intensity at New York, (that at Philadelphia being considered 

 unity,) was found, by observations in common air, .97202; by observations in 

 rarefied air, .94702. Mean of the two determinations, allowing each its proper 

 weight, .94705. My own result is .96707. The horizontal intensity at Pro- 

 vidence, by President Bache's observations, is .89869; by my own, .89830. 



Magnetic Dip. 



The following observations of the dip in different azimuths were made with 

 the same instrument formerly described, for the purpose of testing the axles of 

 the needles. They were made at Hudson, from August 27 to September 4, 

 1840, on the same spot formerly employed. The same mode of observing was 

 adhered to, and each number in the two columns headed "Poles direct," "Poles 

 reversed," is the mean of twenty readings, five being made of each pole in one 

 position of the needle, and the same number after the needle was reversed upon 

 its supports. Thus, 1360 readings were made with each needle. The dip is 

 deduced from the formula cot.^ 8 = cot.^ i + cot.'' ^'. 



VIII. — R 



