280 A. C. Twining—Aurora of Feb. 4th, 1872. 
tion had increased to 50’, where it remained unsteadily for six 
minutes, and thereafter advanced to 65’ increase at 10" 20" 
Resting about at this four minutes, it suddenly reached an 
an eastern variation of 93’, and, at 10" 26", of 113’. Declining 
back however, in 1™ to 52’, it kept traversing, through a range 
of 10’, at about that average till 10" 35", when observation was 
suspended an hour and eighteen minutes. On renewed obser- 
vation, at 11" 53™, the same was found at 1338’ eastern devia- 
tion. It started on in 12™ to 173’, and so traversed till just 
before noon. At 1™ before 12 o'clock it started on to 193’, and 
traversing through a back and forward range of 18’, advanced, 
* 6™ P. M., to 313’, and, at 12" 7, to 328. At this instant 
the north end of the needle—which has, normally, 11° of decli- 
deviation followed by as many of sudden change back agail,— 
that the extreme fluctuation was 5° 40’ in three hours time, a 
that the violent disturbance preceded the visible, although per 
haps not the actual, phenomena. Bie 
Reverting, in conclusion, to the enquiry concerning 
actual height of the zone of 187 2, although the early ee 
tions at Hudson, New Haven, and Haverford, as already admit: 
ted, are not favorable for its determination, yet it is evident, 0 
named the very latest are so nearly coincident as to time, and 
ose stations (158°7 miles) as a base, and the azimuth of the base 
54° W. of m 
zone at the star Sirius, the parallax is found by measure 
ment on the globe to be 9° 5 ith d 
New Haven is found 36° 40’, and the corresponding zenith a. 
tance 65° 10’, and the zenith distance at Haverford 57 - 
