THE AURORA. 317 
cumulated masses from the northwest to the south- 
eastern horizon, forming to the northward an arch of 
some regularity. From the inner circumference of 
this great arch proceeded a series of scintillating proc- 
esses, at apparent right angles to the plane of the 
horizon, and constantly shifting their positions, so as 
to produce an effect nearly like that of the " merry dan- 
cers." To the south, however, the arch hecame irreg- 
ular and changing; its diameter varied from five to 
thirty degrees, the augmentation being by a broken 
series of parallel bands, no one exceeding six or eight 
degrees. 
At the period of its greatest intensity, 7h. 10m., it 
enveloped Procyon and the Pleiades, obscuring the 
larger portion of Taurus, and actually hiding Alde- 
baran. A process extended obliquely from about 
twelve degrees above the horizon to Castor and Pol- 
lux, whose brightness it sensibly dimmed. The zone 
then narrowed, passing about eleven degrees to the 
west of Polaris, and ascending in a regular arch to 
the northwest. It faded gradually, and by 9h. 20m. 
had disappeared. Neither a silk-suspended magnetic 
needle nor our rude electrometers detected any dis- 
turbance. 
The foggy segment which forms the characteristic 
feature of the incipient aurora, as observed by Biot, 
Mairan, Lottin, and others, was in a rudimentary form 
visible with us. The deep bistre-colored arc, which 
I have arbitrarily spoken of as 'No. 4, is in many of its 
features analogous to that of the Shetland and Bosse- 
kop Observations. 
• The well-known aurora of Mairan begins with a 
dark mist or foggy cloud to the northward, not unlike 
the "bistre-colored segment," taking gradually an arc- 
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