APRIL, 1820. MAY
Days. 8 A M. 1 P.M. 4 PM.. 12 P. M. Days. 8 A. M. i p.M..’ 4 PM. 12 P. M.
' ' t 1 , Q , H. '■ 1 17 16 17 s 17- 9 17 0*
2 2 - 17 34* 17 9 17 10 16 52*
3 3 17 17 17 8 17 9 l 17 14
4 4 17 16 17 8 17 8 17 14
5 5 17 16 !17 7 17 7 17 14
6 17 16 17 7. 17 7 17 14
7 17 15 17 7 17 7 17 15
8 17 17 17 8 17 8 17 15
9 17 17 17 8' 17 8 17 15
10 17 18 17 9 17 9 17 16
11 17 17 17 8 17 8 17 15
12 Q - H I 12 17 18 17 8 17 8 17 15
13 17 14 17 9 17 10 13 17 16 17 3 17 8 17 16
14 17 13 17 8 17 8 17 11 14 17 18 17 S 17 8 17 15
15 17 15 17 8 17 10 17 14 15 17 18 17 8 17 8 17 16
16 17 15 17 9 17- 11 17 14pS 16 17 18 17 S 17 8 17 15-
17 17 16 17 9 17 11 17 16 17 17 17 17 9 17 9 17 15
18 17 17 17 9 17 11 17 15 18 17 17 17 9 17 9 17 14
19 17 16 17 10 17 12 17 28* 19 17 17 17 8 17 9 17 16
20 17 16 17 9 17 11 17 1* 20 17 IS 17 8 17 8 17 15
21 17 16 17 10 17 8 17 10 21 17 17 17 8 17 8 ' 17 15
22 17 16 17 9 17 11 17 15 22 17 18 17 8 17 8 17 16
23 17 23 17 S 17 9 17 14 23 17 19 17 9 17 10 17 33*
24 17 17 17 9 17 10 17 15 24 17 25* 17 8 17 9 17 14
25 17 17 17 10 17 12 17 14 25 17 17 17 7 17 7 17 13
26 17 16 17 9 17 9 17 14 26 17 16 17 7 17 7 17 14
27 17 16 17 9 17 • 7 17 13 27 17 17 17 7 17 7 17 14
28 17 16 17 S 17 9 17 14 • 28 17 17 17 7. 17 8 16 54*
29 17 16 17 8 17 8 17 14 29 17 16 17 7 17 8 17 14
30 17 15 17 7 17 7 17 14 30 17 17 17 7 17 7 17 14
31 17 16 17 7 : 17 . 7 17
“ I
* W here th e figures are m arked w ith a n asterisk, th e A u ro ra h ad approached, or p assed, th e zenith, and
w as doubtless th e cause o f th e increased or dim inished variation. T h e variation assum ed for th e 12th of
F e b ru a ry , is, th a t w hich w as observed by M r. F ra n k lin in N ovem ber, th e coldness o f • th e w e a th e r n o t
afterw ards p erm ittin g th e use of instrum ents, u n til th e m onth of F e b ru a ry . I t m ay b e rem a rk e d ; th a t the
g re a te st v ariatio n , w as found betw een 8 a n d 9 A . M ., a n d th e least a t I P . M . T h e needle w as n early
sta tio n a ry d u rin g th e h e a t o f th e day ; a n d th e v ariatio n , then, g ra dually increased u n til th e n e x t m orning.
I f th e needle h ad n o t been affected b y th e A u ro ra, a n d b y som e unavoidable unsteadiness, th e variations
w ould probably have b e e n m uch m ore reg ular. T h e m ost strik in g circum stance in rthese observations is,
th a t though th e needle varies, and is statio n ary , a t th e sam e hours here, in L ondon, and a t S um atra, the
law s w hich g overn it are exactly re v e rse d ; th e variation here bein g g re ate st a t th e coldest period, instead
o f le a s t; and vice verst. F o r th is phenom enon, it is not, perhaps, difficult to account on D r. L o rim e r’s
principles.
T h e an n u al variation seem s to b e inconsiderable.
T h e variations o f th e dipping needle w ere, also, observed; b u t th ey differed very unaccountably. T h e
am ount v aried from 10' to 2 5 '; a n d th e dip w as generally le a st in th e m orning, a n d g re a te st a t 3 P . M .
No. III.
OBSERVATIONS ON THE AURORA
A T F O R T E N T E R P R I S E ,
EXTRACTED FROM THE JOURNAL OF CAPTAIN FRANKLIN.
T he forms of the Aurora Borealis, during the winter, have been so various
and fleeting, that it is impossible to comprehend them in a general outline.;,
and the inferences I have drawn on a subject, respecting which I had not prepared
my mind by previous , study, are offerpd with diffidence; but I hope the
observations of the position of the needle, given in the following tables, may,
together with those, made with great attention by Mr. Hood, be found useful to
such persons as are more conversant with such inquiries.
The horizontal compass was placed in a firm-sheltereci stand, fixed to the
back wall of the house, three feet above, the ground, on a northern exposure,
and the dipping .needle was similarly fixed to the end of the store-house, at the
distance of forty feet. There was no iron near either of them, the house stands
on a sand hill, and there were.no large stones in its immediate vicinity*.
The horizontal compass belonging to a small variation transit, made by Dol-
lond ; and its graduated circle of one and a half inch radius, is divided into de*
grees, the degrees counting from, the north by east and south towards the west to
three hundred and sixty. Each degree is sub-divided to twenty, but by the
assistance of a magnifying glass I could read off accurately, to within three
minutes. The horizontal position was preserved by means of a spirit level
* The Kater’s Compass, with which Mr. Hood made his observations, was fixed in a room on
the opposite side of the house, close to a parchment window that admitted the air, and it was
about twenty-four feet apart from the horizontal compass.