De la Rive on the Aurora Borealis. 365 
This observer, during the day after a night in which he had wit- 
nessed a brilliant aurora, having observed an oscillation of the 
stars as seen with his lens, perceived in the sky rays of a white 
quivering light which rose from all points in the horizon towards 
the pole of the dipping needle, where they formed a light and 
whitish corona like that which the most brilliant aurora presents 
at night. Arago, on consulting old records at the observatory, 
found that there were cousiderable magnetic disturbances that 
day in the magnetic needle kept for showing the diurnal varia- 
tion, thus proving beyond question that the phenomenon observed 
by Dr. Usher was a veritable day aurora. 
I find also in the account of the voyage of the Venus by M. 
de Tessan, that M. Cornulier, an intelligent officer in the French 
Navy, often observed on the coast of New Holland a partic- 
ular direction in the cirrus clouds during the day, from which 
he was enabled always to announce a fine aurora australis at 
hight. M. Cornulier, like M. Verdier, was convinced, from a study 
of the arrangement of the cirrus clouds, that in those regions, 
auroras occur during nearly every day, and that the variation is 
only as to their brightness; they are often hid from view by 
clouds and storms. This remark agrees with the observations 
made under the direction of Captain Lefroy in Canada, at 13 dif- 
ferent stations, and with others, collected by the Smithsonian In- 
stitution. It results from all these observations, that the aurora was 
seen on almost all clear nights, when the moon was not too 
bright, although not at all the stations. This is especially true 
uring the months when the nights are longest. From October 
to March, there is scarcely a night without a visible aurora; and 
they are most brilliant in the month of February. The tables 
show that auroras were seen during 261 nights in 1850, and 207 
in 1851. It is also remarkable and natural, that the auroras 
should have been seen most frequently in the stations nearest the 
magnetic 
ci 
One or the other succeeded the aurora. The appearance of lunar 
t. x . . 
ut the most important proof of the electrical origin of the 
aurora is that derived from its action on the magnetic needle. 
e observations by Arago at the observatory of Paris,* by Fors- 
ey ou de Ch. et de Phys, x. 120; xxx, 423; xxxvi, 398; xxxix, 369; xlii, 3515 
» *Vo. ‘ 
