OF ARTS AND SCIENCES. 381 



ridional bands, and impressing upon them a movement of rotation, as 

 exhibited in De la Eire's experiment; and mentioned the ingenious 

 suo'o-estion of Grove, that the height of the aurora above the earth's 

 surface might perhaps be inferred from a knowledge of the degree of 

 rarefaction at which like luminous effects were obtained in the vacuum- 

 tubes. 



In connection with the jiuorescent influence of the light of some of 

 the tubes, he mentioned the fact, that, during the bx-illiant auroral 

 displays of August and September last, he found that a solution 

 of sulphate of quinine showed its characteristic fluorescence quite dis- 

 tinctly when exposed during the height of the illumination. 



In regard to the straiified character of the discharge, as exhibited so 

 strikingly in some of the experiments, Professor Eogers remarked that 

 this phenomenon, supposed hitherto to belong exclusively to the cur- 

 rent of the induction coil, has recently been produced by Gassiot 

 with machine electricity, and with the continuous current of a vol- 

 taic battery of very high tension. As to the conditions in which the 

 stratification originates, physicists are as yet undecided. The grada- 

 tion of the phenomenon in different stages of exhaustion does not seem 

 to have been sufficiently considered, and would naturally suggest an 

 hypothesis which may not be unworthy of attention. 



When the experiment is made, while the process of exhaustion is 

 going on, the following stages in the effect may be observed: — 



1. While the rarefaction is yet very incomplete, the tube is dark, and 

 no current transmitted. 



2. When the exhaustion has advanced to a certain point, the current 

 passes and the tube becomes filled with a colored electrical light, which 

 as yet shows no appearance of stratification. 



3. At a still higher stage of rarefaction, the column of light begins to 

 exhibit a multitude of extremely thin closely contiguous strata, discern- 

 ible with a magnifier before they become apparent to the naked eye. 



4. As the rarefaction is pushed still farther, these strata become 

 larger and more distinct, with wider intervals of comparatively obscure 

 space between them. 



5. Approaching the extreme limit of exhaustion, a few waves occupy 

 the whole extent of the tube, and finally the light ceases as the current 

 fails to be transmitted. 



In view of these facts, may we not believe that, in every case where 



