METEOROLOGY. 435 



ever takes place at any considerable elevation above the earth's surface. 

 On the one hand observations are cited giving a not unfrequent eleva- 

 tion of nearly 200 miles, while, on the other, experiments with vacuum 

 tubes appear to limit the range to less than forty miles. The observa- 

 tion is, perhaps, a doubtful one at best; it is not easy to fix the position 

 of so faint and flickering a phenomenon, and it is perhaps even more 

 difficult to identify a particular phase of it, when seen from two distant 

 positions." {Nature, xxv, p. 543.) 



J. E. Capron, in some remarks on the aurora and the spectrum, says: 

 "I again plead the necessity for spectrum observation; it is certainly 

 possible that some gas may exist in the upper regions of the aurora 

 giving rise to the citron — perhaps to the red — lines, but it still remains 

 an unexplained fact that such a gas has hitherto failed to be recognized 

 in any other body, celestial or terrestrial. The electrical discharges in 

 vacuum tubes, as tested by Professor Stokes' prism and slit, no more 

 represent the aurora than did the cirrus cloud illuminated by the light 

 of the moon. I would invite all spectroscopists armed with suitable 

 instruments, persistently to retain accurate micrometer readings of the 

 aurora spectrum. The approximate places of the lines are pretty well 

 established; but their actual length of wave positions is much wanted." 

 {Nature, xxv, p. 53.) 



!N^ordenskjold, at the Vega winter quarters, observed but rarely any 

 brilliant aurorie, but the more remarkable phenomenon consisted in a 

 luminous halo-like arc, not distributed into rays, and characterized by 

 its feeble brilliancy as well as by the remarkable quietness of the whole 

 phenomenon; this was nearly always visible on the northeastern part 

 of the horizon, its summit being at an altitude of from 5 to 12 degrees. 

 Hour after hour and day after day this arc remained unchanged; figura- 

 tively it was accompanied by one or several exterior arcs. His obser- 

 vations and measurements have led him to the following conclusions as 

 to the nature of aurorae: "Our globe," he says, "even during a mini- 

 mum aurora year, is adorned with an almost constant crown of light, 

 single, double, or multiple, whose inner edge was usually, during the 

 winter of 1878-'79, at a height of about 0.03 radius of the earth above its 

 surface; whose surface was somewhat under the earth's surface, a little 

 north of the magnetic pole, and which, with a diameter of about 0.32 

 radius of the earth, extends in the plane perpendicular to the earth's 

 radius and passing through the center of this luminous ring." {Nature, 

 XXV, p. 321.) 



Nordenskjold concludes that there are five different regions situated 

 around the aurora pole where the glory would appear under quite differ- 

 ent aspects. In the first circular region within 8° of the aurora pole, 

 the glory is visible only as a luminous mist or a very low bow in a 

 direction opposite to the aurora pole. In the second region between 8° 

 and 16° region, the common ring of aurora must be seen as a luminous 

 bow, the upper part of which is opposite the aurora pole. In the third 



