396 Prof. Kirkwood on the Aurora of 1859. 
observed the motion was estimated as being fully 20° per min- 
ute. The ever varying wisps of cloud at the corona, and the 
southern streamers were also moving to the east. I left the dis- 
play in full action without observing farther. 
The repetition which took place Sept. 3d, ene on a vastly 
diminished scale of grandeur, I observed about 0 e hour,—sa 
from 94 to 105 p.m. It was remarkable for the charaies of the 
auroral waves, which passed upward, ees engge gone 
different definite spaces in their path. The mo of thes 
waves was far more moderate than I have ever sane reunarigas 
Tn this instance I could not a it to exceed forty-five de- 
grees of arc in a second of time. The movement was every- 
where distinctly upward; but the ‘det&rmination of arcual or an- 
ar motion in this phenomenon, i is excessively difficult and in- 
exact. 
5. Two letters from Prof. Daniel Kirkwood, Bloomington, Ind. 
[ First letter.] 
Aug. 29th, 1859. 
TO THE EDITORS, &c. 
Genilemen :—The most extraordinary display of the Aurora 
Borealis I have ever witnessed was seen from this place last 
night. It was observed immediately after the close of twilight, 
and, in the course of an hour, the whole northern horizon from 
east, to west was illuminated. The phenomenon continued from 
stars Alioth, Micab and where it to orm of 
streamers, ie wide a point somewhat south of the 
zenith. At the same time an arch of light appeared, havin 
one extremity in the horizon beneath, or rather westward of, 
almost of necessity the declination and dip; which seem to be merely resultants of 
all the electro-dynamic actions upon the needle, subsisting at the time. Under the 
above hypothesis, therefore, every development of streamers must ordinarily concur 
Pe hae other phenomena, viz., a lateral movement of the streamers, a of 
cial ages Sapte Be 
gratuitous. It is only ite that the medium, or substance through or along 
which the current passes, shall be eS of illumination 0 — hare oe so 
‘ain phenomena however indicate that t trans uroral vapor lat- 
erally with itself. The importance of Of this clas bf abonrations to questans Fel? 
ting to the cause of the aurora, as well as to the direction of currents, is obvious. 
