* 
142 <A. D. Bache on Magnetical Observations in Maine. 
long, ,%; inch external and 4 internal diameter; value of a 
scale division 15”, The dip-circle has a diameter of 54 inches, 
and reads to 30” by sian: of two verniers; io eee are 94 
inches long, and the ntings are made w microscopes 
attached to the vuonicas on small holes liam through the 
needles. Those use during the first half of the series have 
axles and pivots of the ordinary construction, but from October 
1862 two needles were used having their axles so fitted in 
arbors, as to admit of being turned about their centers, by 
rich means they may be brought to rest on different parts of 
the pivots. The observations were made on each day in three 
different positions of the pivots, and the errors arising from 
faults in their figure appear to be very nearly eliminated. 
The position of the magnetic observatory is on the parade 
ground of Fort Sullivan near Eastport, in lat. 44° 54’-4, long. 
66° 58'°9, west of Greenwich. 
he observations were made successively by Messrs. G. B. 
Vose, S. Walker, E. Goodfellow, A. T. Mosman and H. W. 
Richardson, all attached to the Coast Surve 
The discussion herewith presented of the ec Sigs et has 
been made by Assistant C. A. Schott. The results are stated 
under the several heads of declination, ai: ad horizontal 
intensity 
1. Padnaten: —The zero of the emg magnet, or the 
position of the magnetic axis on its scale, was determined by 
inversions each month, and its readings on rite circle referred to 
a distant mark of known azimuth. On four days about the 
middle of ich month the declination readings were recorded 
every half hour, between the morning minimum and the after- 
noon maximum, generally between the hours of 6 A. M. and 2 
P.M. Hach monthly declination result is therefore the mean 
from observations made on four days. 
To obtain es mean declination of the day or that value 
which would result from 24 hourly observations, a small cor- 
greatest declination of the day gives the west declination too 
large, as does also the — of the half hourly readings between 
those extremes, the amount of excess being the same. We 
have << the following corrections to our means expressed 
tn parts of the diurnal range: 
fe ee ee 
“ February. ~ “ August, es 
March, : — sy % September, —_ sls 
. April — Pi * « Octo : ine 
0 
