METEOROLOGY AND ALLIED SUBJECTS. 'dl3> 



mate to conclude an intimate connection between tbc aurora and zodiacal 

 light. Similar observations have been made by Otto Struve, Wiulock^ 

 Fliigel, Ellery, Lindsay, Barker, Vogel, Browning, and others, who have 

 been able with more perfect apparatus to increase the number of auroral 

 lines aad bands up to fifteen or twenty, all of them, however, much fainter 

 than Augstrom's line, which is usually spoken of distinctively as the 

 aurora line. Angstrom has suggested a theory according to which 

 the apparent spectrum of the aurora consists of two different spectra 

 superposed, one of monochromatic yellow light peculiar to the aurora^ 

 the second, identical with the spectrum of the light at the negative pole 

 of a platinum electrode immersed in dry air rarefied to a pressure of 

 only a few millimeters. Some observations upon the spectrum of the 

 solar corona have led to the suggestion that the auroral light is nearly 

 identical with that of the corona ; but observations on this point are 

 contradictory, and the conclusion is not generally accepted. 



(153) The spectra of the November meteors, as observed by Browning,, 

 lias considerable similarity with that of the aurora, as also has the spec- 

 trum of the lightning, from all of which it is rational to suspect that the 

 atmosphere of the earth has an important part in determining the char- 

 acteristics of the spectrum of the aurora as well as in the formation of 

 the aurora itself; but all definite conclusions as to the origin and nature 

 of the aurora must be withheld for the present. 



(24) In the twelfth chapter Fritz exposes the present state of our 

 knowledge as to the much debated question of the noise accompanying 

 the aurora. The opposite views held by so many i>romineiit observers 

 are carefully weighed by him with the following conclusion : "This showtj 

 satisfactorily how great a part of the noises heard during the auroras 

 depend upon self-deception ; especially do the cases in which the noise 

 and the light ought to appear simultaneously prove how very mislead- 

 ing the appearances are. If such observations are not the result of 

 deception, then the noise should spread through the upiier regions of 

 the atmosphere, and distribute itself in the higher latitudes." 



To substantiate his hypothesis he constructed an aurora apparatus; 

 but in this at the two Poles he produced very different phenomena cor- 

 responding to electricity of opposite signs, so that if his apparatus cor- 

 responded to nature the northern and southern auroras ought to present 

 very different appearances, which, however, is not the case. His appa- 

 ratus therefore only imitates the outward appearance of the auroral 

 rays, which can be made to vary in the most striking and brilliant 

 manner by the increase or decrease of the vacuum employe<l in the 

 apparatus, or by the introduction of various gases or vapors. 



The hypothesis of George Fisher, London, 1834, has becni widely 

 adopted, according to which the aurora is an electric discharge between 

 strongly electrified masses of ice or snow crystals, formed in the neigh- 

 borhood of extensive fields of ice or snow, where the aqueous vapor is 

 being most rapidly condensed ; but we must still consider it an open ques- 



