Proceedings of Scientific Societies. 379 



case, 30°, and each series included 320 oscillations, the instant of the 

 completion of every tenth vibration being noted. No correction, there- 

 fore, is applied for the arc of vibration. The times vi^ere observed at Dor- 

 chester, Princeton, and Philadelphia, by a chronometer, and at the other 

 stations by a lever watch, which, at Hudson, was compared with the ob- 

 servatory clock before and after the observations. The author remarks, 

 that " at the remaining stations there is a little uncertainty with regard 

 to the time, yet it is thought its influence upon the results will not be 

 great." 



The correction for temperature, for each of the needles, was obtained 

 by direct experiment, and gave the following coefficients : — 



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

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

 to a standard temperature of 60° Fah. 



The author gives the reasons which induce him to apply no correction 

 for the change of magnetism in the needles. The observations for hori- 

 zontal intensity were principally made in September and November, 1839. 



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

 erly 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, combined with the 

 dips formerly observed, the author gives the total intensities, taking New 

 York as 1.803, according to the determination of Major Sabine, and re- 

 ferring to the unit established by Humboldt, as follows : — 



The author remarks that Hudson, Ohio, and New York, thus appear to 

 have sensibly the same magnetic dip and intensity. He concludes this 

 part of his memoir with a comparison of his intensity observations with 

 those of Professors Bache and Courtenay. 



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

 vations 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 nee- 

 dle No. 1 were quite satisfactory, and for needle No. 2, showed a diifer- 

 ence in the extremes of 12.7' : upon a review of the whole, the author con- 

 siders them as justifying confidence in the needles used. 



The following determinations of the dip are next given : — 



