10 LIGHT SCIENCE FOR LEISURE HOURS. 



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 

 atmosphere. 



Both the considerations above discussed are of the 

 utmost importance in studying the subject of the auroral 

 light as analysed by the spectroscope, because there are 

 many difficulties in forming a general opinion as to the 

 nature of the auroral light, while there are circum- 

 stances which would lead us to anticipate that the light 

 is electric. 



I notice also in passing that we owe to the Swedish 

 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 presently 

 see why I have brought Angstrom's name prominently 

 forward in connection with the interesting branch of 

 spectroscopic analysis just referred to. If the discovery 

 we are approaching had been effected by a tyro in the 

 use of the spectroscope, doubts might very reasonably 

 have been entertained respecting the exactness of the 

 observations on which the discovery rests. 



It was suggested many years ago, long indeed before 

 the true powers of spectroscopic analysis had been 

 revealed, that perhaps if the light of the aurora were 

 analysed by the prism, evidence could be obtained of 

 its electric nature. The eminent meteorologist Dove 

 remarked, for instance, that 'the peculiarities presented 



