1889.] of the various Species of Heavenly Bodies. 247 



aurora is furnished by other phenomena, which sometimes accompany 

 them. 



During the great aurora of January, 1831 (Poggendorffs ' Annalen ' 

 of that year), a bright yellow streak was seen to rise with common 

 cloud velocity, forming an arch from west to east, becoming invisible 

 in the west by the time it had reached tbe east. 



During the same aurora Professor Bischoff, at Burgbrohl, saw a 

 moving cloud, as bright as the Milky Way, pass from east to west in 

 five minutes. 



During another aurora, December, 1870, Professor Rudberg, of 

 Upsala, saw a very bright patch, of double the dimensions of the 

 moon's disk, moving with great velocity behind the auroral beams. 



On November 2, 1871, Dr. Groneman saw a strange, feather-like, 

 brilliant arch, striped parallel to its well-defined sides, and changing 

 its curve during its visibility of two hours' duration. Dr. Vogel 

 determined the auroral character of its spectrum.* 



On May 17, 1875, Mr. Lefroy (Freemantle, Western Australia) 

 describes a similar feather-like appearance, which he considered to be 

 converging streams of infinitely minute particles of matter passing 

 through space at a distance from the earth less than that of the moon, 

 and at which the earth's aerial envelope may still have a density suffi- 

 cient, by its resistance, to give to cosmic dust passing through it with 

 planetary velocity that slight illumination which it possesses. f 



On November 17, 1882, however, was seen the most remarkable 

 display of this nature in the middle of an intense aurora then visible. 

 Again the appearance was feather-like, again the spectrum was auroral, 

 but the strange object moved across the sky, at a height of 133 miles, 

 as determined by Capron and Herschel, and with a planetary velocity 

 of between 10 and 15 miles a second ! 



Dr. Groneman did not hesitate at the time to look upon it as a mass 

 of meteoric dust traversing the higher reaches of our air, and 

 regarded it as a strong confirmation of the view which he had resusci- 

 tated,}: a conclusion in which I concur. 



The above results also strengthen the view that the aurora is very 

 similar in some respects to the zodiacal light. Such a connexion is 

 indicated by the fact that when we have greatest number of aurorae, 

 in spring and autumn, the zodiacal light is also best visible. The 

 spectroscopic observations of Angstrom and Respighi show that the 

 spectrum of the zodiacal light consists of the characteristic line of the 

 aurora and a short continuous spectrum, and thus furnish further 

 evidence of the connexion suggested. The observations of Wright 

 and others, showing that the spectrum is continuous, are not at 



* ' Nature,' vol. 27, p. 297. 

 f ' Nature,' vol. 12, p. 330. 

 J ' Nature,' vol. 27, p. 296. 



