THE AURORA. 17 



pany the record of such an observation with an expres- 

 sion of doubt as to the real nature of the object which 

 is the source of light. 



Secondly, when an electric spark flashes through 

 any vapor, its light gives a spectrum which indicates 

 the nature, not only of the vapor through which the 

 spark has passed, but of the substances between which 

 the spark has travelled. Thus, if we cause an electric 

 flash to pass between iron points through common air, 

 we see in the spectrum the numerous bright lines which 

 form the spectrum of iron, and in addition we see the 

 bright lines belonging to the gases which form our at- 

 mosphere. 



Both the considerations above discussed are of the 

 utmost importance in studying the subject of the au- 

 roral light as analyzed by the spectroscope, because 

 there are many difficulties in forming a general opinion 

 as to the nature of the auroral light, while there are 

 circumstances which would lead us to anticipate that 

 the light is electric. 



We notice also in passing that we owe to the Ger- 

 man physicist Angstrom a large share of the researches 

 on which the above results respecting the spectrum of 

 the electric spark are founded. The reader will pres- 

 ently see why we have brought Angstrom's name prom- 

 inently forward in connection with the interesting 

 branch of spectroscopic analysis just referred to. If 

 the discovery we are approaching had been effected by 



