200 
the earth’s atmosphere would acquire a velocity of rotation with 
the earth ; electric currents would thus be generated owing to 
different parts of this medium cutting the earth’s magnetic lines 
of force at different angular velocities; and the currents thus 
generated would be of the direction required to account for the 
perturbations of the magnetic needle. Such currents would 
also produce earth currents. The notion of meteoric haze being 
that which causes the Aurora may be connected with the fact 
that of 19 displays of Aurora selected from upwards of 250 
during 13 years as being very brilliant, five occur on or about 
the 17th of November; and on ten of the 13 years there was 
an Auroral display at that time. The spectrum of the Aurora 
coincides with that of the zodiacal light and with that observed 
in a sky filled with luminous haze. Of Auroras observed at 
Dunse from 1840 to 1850- seventy-five were connected with 
stratification of cirrus clouds, the stratification of such clouds 
being parallel to the magnetic meridian while they moved 
slowly from S.W. to N.E. In those Auroras which have a 
“corona” it is in the prolongation of the direction of the mag- 
netic dip. During an Auroral display the line of the dip seems 
generally to become more vertical. 
Professor CHALLIS corroborated the account of the cloud 
coming and going, which on one occasion had been seen by 
himself at Cambridge, and Sir John Herschel at Collingwood. 
He had calculated the height of an Auroral arch at 175 miles. 
The streamers, he believes, go up hundreds of miles. The other 
phenomena mentioned by Mr Stuart about 175. The apparent 
convergence of the streamers is only an effect of perspective. 
He considered the streamers magnetic, and the Aurora pro- 
duced by transverse streams. That there were two kinds of 
Auroras, one local, the other due to extraneous action. The 
Astronomer Royal had found that only the latter corresponded 
with disturbance of the needle. Auroras are said to be very 
common at Behring’s Straits. 
