524 
Daily Variation. 
1859. 
Dip. Bifilar. 
April 21, + 27'°47 - 485°0 Aur. Bor. evening. 
» 22, + 7°04 2 181°7 Ditto. 
, igal Aur. Bor. could not be seen for the 
Jnne 8, + 17°02 — 295°9 crepuscnlum. 
July 11, + 16°66 | - 268-5 
BED 1G) Sp 4 9 “aR > Senet 7 
August 22,. .{ + 7°51 — 133°9 21, Vehement Aur. Bor. evening ; 
” 9,. .| + 11°76 - 179-1 28, and midnight. 
September 2,..} + 82 :03 — 801°3 J 
October 18,. .| + 19 *69 — 355°7 : 
ag 4 16 21 a 250-4 Aur. Bor. 17, 18, 20, evening. 
1860. 
February 21, . 4-08 — 168°2 Aur. Bor. evening. 
May 24,.. .| + 8-97 — 180°8 
ae 
“‘ Kvery time that I saw in the evening observation, in my tent, an 
extraordinarily small dip, I was sure that the Bifilar marked a strong 
horizontal intensity, which never failed. The Bifilar variation above given 
is the difference of parts of the scale (forenoon — afternoon). For in- 
stance :— 
Dip. Bifilar. * 
September 2, .| 105 23™ 4.m., 71° 29':01 637 °56 
” 4h 16™ P.m., 70 26 ‘98 1438 °91 
Difference, . .| +1 2°03 — 801°35 
‘One part of the scale of the Bifilar=+537, of the horizontal inten- 
sity. 
‘* HANSTEEN.”” 
Dr. Lloyd communicated also to the Academy the following extract 
from a letter from Professor Hansteen, dated April 17, 1861 :— 
‘* At our interview in Christiania, in July, 1860, I communicated 
to you the mean daly variation of the magnetic dip in this place be- 
tween its maximum at 10 a.m., and its minimum, about half an hour 
before sunset, for every month in the year, deduced from different years 
between 1844 and 1859. This variation, which at the winter solstice 
was only a fraction of a minute, increased very regularly to a little more 
than three minutes towards the summer solstice, and decreased again as 
gradually towards December. 
“Tn order to ascertain if there is a monthly variation of the dip in the 
course of the year, I began, from April, 1855, to observe the dip in its 
daily maximum and minimum, generally five or six days about the 
middle of each month, to this year. The mean of the daily maximum 
and minimum, is contained in the following Table :— 
Fe 
