152 
From the agreement of repeated observations, it is inferred that 
the uncertainty of the observations at a particular spot does not 
exceed one or two minutes of arc in the declinatior and dip and 
one five-hundredth part of the horizontal force.’’ The results ob- 
tained are given in a table, showing, in parallel columns, ‘ the 
- Jatitude and longitude of the stations, the declination, dip and 
horizontal intensity of the earth’s magnetic force, the date of the 
observations and a reference to the particular locality, its geology 
and other attending circumstances.’’ * 
At the Springfield meeting in 1859, Professor Bache presented 
to the American Association a paper entitled ‘‘ General Account of 
the Results of the Discussion of the Declinometer Observations 
made at Girard College, Philadelphia, between the Years 1840 
to 1845, with Special reference to the Elevén-Year Period.’’ 
‘“‘In codperation,’’ he says, ‘‘with the scheme adopted at 
the British colonial observatories, a series of magnetic and meteor- 
ological observations were made at the Girard College Observatory 
with instruments purchased under the direction of the trustees of 
the College, the observations being made under the patronage 
of the American Philosophical Society, and finally completed for 
the use of the Topographical Bureau of the War Department. 
These observations were made under my direction and superin- 
tendence. ‘The series commenced in May, 1840, and, with short 
interruptions, terminated in June, 1845; thus furnishing a five 
years’ series of magnetic observations taken bi-hourly up to 
October, 1843, and after that date hourly. .... It is proposed 
especially to investigate the law of the eleven-year period, or, as it 
is more frequently called, the decennial period, there being yet an 
uncertainty as to its precise length. It is supposed to have some 
direct or indirect connection with the solar spot period, which cor- 
respondence, according to late investigations by Prof. R. Wolf, is 
so close as to exhibit even analogous disturbances.’’+ Mr. Schott’s 
mathematical discussion of these observations gave results showing 
plainly the inequality constituting the ten or eleven-year period, 
the year 1843 being directly indicated as the a) of the minimum 
range of the diurnal fluctuation. 
Two papers dealing with the phenomena of Terrestrial Magne- 
tism were presented by Professor Bache to the American Association 
at its meeting in Newport in 1860. The first of these was a ‘‘ Gen- 
* Proc, Amer. Assoc. Adv. Science, x, 187, 1856. 
+ Ibid., xiii, 248, 1859. 
