309 



For the Hansteen needle, .000191; for the Sabine needle, .000328 ; 

 for the Henry needle, .000116. The results of observation are re- 

 duced to a standard temperature of 60° Fah. 



The author gives the reasons which induce him to apply no cor- 

 rection for the change of magnetism in the needles. The observa- 

 tions for horizontal intensity were principally made in September and 

 November, 1839. 



The stations of observation at different places were the same as for- 

 merly described (Am. Phil. Soc. Trans.), except at Dorchester, which 

 was near Mr. Bond's Observatory. The details of the observations 

 are given, and from the mean of those for horizontal intensity, com- 

 bined with the dips formerly observed, the author gives the total in- 

 tensities, taking New York as 1.803, according to the determination 

 of Major Sabine, and referring to the unit established by Humboldt, 

 as follow s: — ■ 





Horizontal Intensity. 





Dip. 



Total Intensity. 



New York, 



.96707 



72° 



52.2' 



1.803 



New Haven, 



.92364 



73 



26.7 



1.780 



Dorchester, 



.88182 



74 



16.0 



1.786 



Providence, 



.89830 



73 



59.6 



1.789 



Princeton, 



.97414 



72 



47.1 



1.807 



Philadelphia, 



1.00000 



72 



07.0 



1.788 



Hudson, 



.97344 



72 



47.6 



1.807 



The author remarks that Hudson, Ohio, and New York, thus ap- 

 pear to have sensibly the same magnetic dip and intensity. He con- 

 cludes this part of his memoir with a comparison of his intensity ob- 

 servations with those of Professors Bache and Courtenay. 



2. Magnetic Dip. — This section commences with an account of 

 observations of the magnetic dip, made at Hudson, Ohio, in different 

 azimuths, to try the figure of the axles of the dipping needles. The 

 results for needle No. 1 were quite satisfactory, and for needle No. 2, 

 showed a difference in the extremes of 12.7': upon a review of the 

 whole, the author considers them as justifying confidence in the nee- 

 dles used. 



The following determinations of the dip are next given: — 



Latitude. Longitude. Date. Magnetic Dip. 



Hudson, Ohio, 4°1 15N. 81 26 W. April 15, 1840 72 53.2 

 Aurora, „ 41 20 81 20 Sept. 8, „ 72 55.5 



Windham, „ 41 15 81 03 „ 8, „ 73 03.4 



