1889.] of the various Species of Heavenly Bodies. 22 $ 



aurora, so that the coincidences are only accidental. The same applies 

 to the bands in the negative-pole spectrum. 



Like Lemstrom, then, Gyllenskiold makes no advance as regards 

 the origin of the spectrum of the aurora, but at the same time it is- 

 only fair to acknowledge the value of the observations. 



I have next to refer to my own observations and comparisons. 



IV. The Sequence of the Flutings and Lines seen in a large Tube at 

 different Stages of Pressure. 



In order to demonstrate that the aurora spectrum does not coincide 

 with the vacuum-tube spectrum of air, I have made a series of obser- 

 vations of an end-on air vacuum-tube, about 5 feet long and 2 inches 

 in diameter. The tube was arranged as in fig. 17, one end being 

 connected with the Sprengel pump, and the other with a piece of 

 glass tube by means of mercury joints. The latter tube was con- 

 nected with a hand air-pump to save time in exhausting. After partial 

 exhaustion the tube was sealed off with a blowpipe, and the exhaustion 

 completed with the Sprengel. The slit of the spectroscope was- 



FIG. 17. Large end-on vacuum-tube, arranged for an observation of the Spectrum 

 of air at varying pressures. 



placed close to the bulb at the end of the tube (fig. 17). The diagram 

 also shows a Geissler tube arranged for comparison. 



