Proceedings of Scientific Societies. 379 
case, 30°, and each series included $20 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 were 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 
toa 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 former] y observed, the author gives the total intensities, taking New 
York as 1.808, according to the determination of Major Sabine, and re- 
ferting to the unit established by Humboldt, as follows :— 
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 
u 97344 72 47.6 1,807 
’ 
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 D ip.—This section commences with an account of obser- 
vations of the magnetic dip, made at Hudson, Ohio, in different azimuths, 
‘0 try the figure of the axles of the dipping needles. The results for nee- 
No. 1 were quite satisfactory, and for needle No. 2, showed a differ- 
*nce in the extremes of 12.7’: upon a review of the whole, the author con- 
Siders them as justifying confidence in the needles used. 
a following determinations of the dip are next given :— 
