THE AURORA. 469 



" nordlicht " in German, " nordljus " in Swedish, and " nordlys " 

 in Danish, all meaning northern lights. 



The aurora in its most varied and interesting forms is either 

 motionless or rapidly and incessantly scintillating. Of the first class 

 there are three forms: (1) Faint lights without very defined form; 

 (2) more distinct, in patches or clouds; (3) clearly defined arcs 

 touching the horizon at either end. Of the second or moving class 

 there are: (4) irregular arcs, formed of intermittent rays; (5) rays 

 isolated from each other at a greater or less distance, converging to 

 a fixed point in the sky, and sometimes forming around this center 

 a crown or glory; (6) non-homogeneous bands, formed of rays 

 pressed close together, which have not all the same degree of bril- 

 liancy; sometimes these bands fold over on themselves, becoming 

 draped auroras, the most beautiful of tlieir manifestations, aside from 

 the boreal crown. 



It sometimes happens that these arcs, instead of being circular, are 

 distinctly ellij^tical; the two curves which form the upper and lower 

 edge of the arc may or may not be parallel; sometimes, instead of a 

 single circular arc, there are two, three, or four arcs, all perfectly 

 concentric. Multiple striped arcs are not uncommon. Stars have 

 been discerned through the rays, as also through the arcs, proving 

 their extremely diaphanous character. 



The chief characteristic of the auroral rays is their extreme vari- 

 ability. They are subject to two kinds of movements: the lateral or 

 sidewise, and the longitudinal or upward; both movements are very 

 rapid. A ray in twenty-seven seconds covered a distance of ninety 

 degrees, or half the heaven, in one instance. At times a ray remain- 

 ing nearly in the same place is seen at the upper extremity to dart 

 toward the zenith or lengthen itself upward. At other times it rises 

 and falls alternately, vibrating, and it is then said to dance. By 

 sixteenth-century writers these rays were called " leaping goats " and 

 " flying fires " ; such rays are still known in Canada as " mario- 

 nettes," and in the Shetlands as " merry dancers." 



The direction of all the rays passes, as a rule, close to the magnetic 

 zenith of the locality, or may radiate therefrom, as we have seen, 

 forming a crown; the center of this crown may be either luminous 

 or obscure. At certain moments the rays which compose this crown 

 or glory enter into rapid movement, become very brilliant, and take 

 on, instead of the usual yellowish-white color, vivid tints of red and 

 green. This is one of the finest auroral effects, if not the finest. 

 When one of these crowns forms in the midst of an already existing 

 aurora, all the other lights of the aurora pale, to reappear when the 

 crown is dissipated. 



So much for the forms of the aurora. Xow as to the colors. The 



