Observations upon Auroral and Optical Phenomena. 221 
exactly similar and similarly inclined. At those portions of the 
streamers which were 20° above the horizon the obliquity to the verti- 
cal was about 17°. These streamers increased steadily in brightness, 
and their remarkable similarity and correspondence of position led 
me to look above, in expectation of finding them to be part of a con- 
nected line. Immediately over head I at once perceived an arch 
forming,—in appearance like a thin whitish vapor—well defined but 
narrow, and so faint that it would not have attracted notice, had not 
its existence been suspected and sought for. This circumstance 
seemed at first to suggest a probability that the bow might be arran- 
ged in a horizontal stratum of vapor, too faintly luminous, and too 
thin to make a strong impression on the eye looking directly through 
its substance, and requiring to be viewed through a section oblique 
to its length, and thus to have its successive parts accumulated upon 
each other, in order to give the impression of brightness. Soon, 
however, the parts over head increased in brightness, as did also 
those towards the horizon,—the part in the west being the brightest, 
and all having the apparent density of a common cirro-cumulous 
cloud. At 9h. 55m. I find by my minutes, made at the time, that 
the arch was centered over head in the star Alpha Lyrae, which ap- 
‘peared undiminished in brightness. At the same time its centre 
passed, in the east, through a star which I take to have been Mar- 
kab, and in the west about 53° to the north of Arcturus, It was 
therefore at this time disposed nearly in a great circle, whose merid- 
jan passed 15° east of north, instead of about 6° west of north, as 
the magnetic direction of the region would have Jed us to expect.* 
At 10h. 5m. the arch was centered in, Arcturus,—then about 20° 
high in the west. Higher up it cut the southern edge of Corona. 
Over head it had moved 52° southward in Lyra. In the east it 
had also advanced southward, but not more than 2° opposite the 
star before mentioned, then estimated to have 25° of altitude. It 
thus appeared evident that the western parts of the arch were in a 
state of more rapid apparent motion than the eastern, or even than 
the vertex,—since a motion of 52° over head would correspond 
(supposing the arch horizontal) to about 2° at an altitude of 20°, 
* — refers be the cnponnidach limb of the arch. ae eastern limb would have its 
the and west ase The arch 
ent fram th 
Was certain} 
Kien oe were, sane hs inclined to the weet while the arch ‘ae a my 
enith. It was much more probably disposed in asmall circl 
cial . 
sed in a sreat vid 
