THE AURORA BOREALIS. 99 



An extraordinary experiment, illustrative of the theory of the aurora similar 

 to that suggested by Faraday, with te addition that " electricity is radiated in 

 a peculiar manner fr>m magnetized bodies," was introduced by Mr. Nott at the 

 meeting of the British Association at Cork (1843). He rotated a steel globe, 

 and passed magnets from the equator to the poles, till the globe was perfectly 

 magnetized. He then insulated the globe, and placed an insulated ring around 

 its equatorial regions. He connected the ring with the prime conductor of the 

 resinous plate of his " rheo-electric machine," and one pole of the globe with the 

 conductor of the vitreous plate. It is necessary to mention, that the machine 

 alluded to consists of two parallel plates, one plass, the other resin, rotating on 

 the same axis, and provided with separate rubbers. The circuit, including the 

 rubbers and conductors, is completed in various ways ; the machine is described 

 as producing a current of electricity of tension analogous to that of the pile. 

 In the present experiment, when the machine is rotated, a truly beautiful and 

 luminous discharge takes place between the unconnected pole of the globe and 

 the ring. A dense atmosphere is more favorable to the success of the experi- 

 ment than a dry one. It had then the appearance of a ring of light, the upper 

 part of which was brilliant, and the under dark : above the ring, all around the 

 axis were foliated diverging flames, one behind the other. 



In Captain Franklin's narrative, the auroras observed at Fort Enterprise, in 

 North America, are described by Lieutenant Wood as follows : 



They rise with their centres sometimes in the magnetic meridian, and 

 sometimes several degrees to the eastward or westward of it. The number 

 visible seldom exceeds five, and is seldom limited tu one. The altitude of the 

 lowest, when first seen, is never less than four degrees. As they advance 

 toward the zenith, their centres (or the parts most elevated) preserve a course 

 in the magnetic meridian, or near to it ; but the eastern and western extremi- 

 ties vary their respective distances, and the arches become irregularly broad 

 streams in the zenith, each dividing the sky into two unequal parts, but never 

 crossing one another until they separate into parts. Those parts which were 

 bright at the horizon, increase their brilliancy in the zenith, and discover the 

 beams of which they are composed, where the interior motion is rapid. This 

 interior motion is a sudden glow, not proceeding from any visible concentra- 

 tion of matter, but bursting out in several parts of the arch, as if an ignition of 

 combustible matter had taken place, and spreading itself rapidly toward each 

 extremity. In this motion the beams are formed. They have two motions : 

 one at right angles to their length, or sidewise, and the other a tremulous and 

 short vibration, in which they do not exactly preserve their parallelism to each 

 other. The wreaths, when in the zenith, present the appearance of corona 

 boreales. The second motion is alwaj T s accompanied by colors ; for it must 

 be observed that beams are often formed without any exhibition of colors, and 

 I have not in that case perceived the vibratory motion. 



The northern lights are sometimes tinged with the various prismatic colors, 

 among which orange and green, but more frequently the different shades of 

 red, predominate. Maupertius describes one seen by him in Lapland, by which 

 an expensive region of the heavens toward the south appeared tinged with so live- 

 ly a red, that the whole constellation of Orion seemed as if dyed in blood. Some 

 observers of this meteor have affirmed that they have heard a rustling or crack- 

 ling sound proceed from it ; doubts have, however, been entertained on this point, 

 from the circumstance that no such noises were heard by Scoresby, Richard- 

 son, Franklin, Parry, and Hood, who observed the polar lights with great care, 

 under the most favorable circumstances, in very high latitudes. But the testimo- 

 ny of other observers is so positive a kind, as to leave no reasonable doubt that ^ 

 the phenomenon has, at least in particular instances, been accompanied by sounds. > 



