August 13, 1885] 
parallel with the inclination needle. The luminous 
matter in these sheets is either even, diffuse, or divided 
into streamers. 
“Everything now depends on the position of the ob- 
server in relation to such a zone in order that it may 
appear in one form or the other. If he be very far from 
the aurora he will see an arc, diffuse or radiating, accord- 
ing to the nature of the luminous matter. If he 
approaches he will most probably see several distinct 
arcs, the phenomenon gathering more force and the 
colours more life ; and when still nearer, the aurora will 
appear as a band, and, if the luminous matter be radiating 
and passes the magnetic zenith of the observer, he will 
behold the auroral corona.” 
He thus holds that a “band” is a near arc occupy- 
ing a higher position in the sky :— 
NATURE 
“The auroral band is oftenest seen in those parts of 
349 
the globe which are considered to be the true home of the 
Aurora Borealis, but seldom, or hardly ever, in southern 
latitudes. What is chiefly characteristic of the band in 
opposition to the arc, although no sharp line of distinction 
can be drawn here either, is its great height above the 
horizon, but at what elevation it ceases to be band and 
becomes arc is naturally an arbitrary determination. The 
band, as well as the arc, may consist of equi-luminous 
matter, of streamers, and of so-called luminous clouds, 
and it is, to a higher degree than is the case with the arc, 
subject to the most violent changes of position, form, and 
motion. Particularly when the band consists of streamers 
it displays the richest variations and greatest beauty, the 
folds of the streaming drapery, the prismatic play of 
colour, and the light-waves, which with marvellous 
rapidity course through the graceful undulating rays, 
forming a spectacle of light, colour, and form which 
C, at 8h. rom. 
Fic. 5.—Phases of an auroral arc, December 1, 1878. 
makes this variety of the Aurora Borealis the most 
charming of all. 
“ The perspective fundamental form of the arc, and also 
the band, may, in my opinion, be explained by the aurora 
forming one or several rings, or fragments of such, which, 
with the magnetic pole as centre, or, more correctly, with 
a point in the magnetic axis of the earth—viz. the straight 
line between the two magnetic poles—lie at a certain height 
above the earth’s surface. On account of the great cir- 
cumference of the earth, in proportion to the height of 
the aurora, only a small portion of such a ring would be 
visible at one time, and each observer only see his own 
portion, the situation of which in relation to #25 horizon 
and the zenith will depend on /zs position in relation to 
the auroral ring.” 
The auroral streamers are closely associated both with 
arcs and bands, an arc or band composed of streamers 
often forming the basis for a colonnade of streamers. 
Before we proceed to the consideration of the corona, 
the following extracts concerning streamers and their 
apparent motions will be read with interest :— 
“The streamers embrace a number of varieties, which 
have only one peculiarity in common—viz. that the direc- 
tion is very nearly vertical, and that the length is always 
greater than the width. The length differs greatly, from 
2° and 3° to 30° and 40° or more. The width is very 
difficult to estimate, on account of the constant motion ; 
a single streamer thus may form only a slender thread of 
light, while others may have a width of from 10’ to I’, or 
more. Short streamers form often, as I have mentioned 
above, bands or arcs. The long streamers gather gener- 
ally in bunches, which may either remain isolated, or 
