EVOLUTION IN THE SUNS 63 



latter elements being absent at the lower 

 temperatures. 



In studying this subject the same element, 

 such, for example, as iron, may be experi- 

 mented upon at different temperatures, and 

 when this is done, remarkable changes are 

 seen as higher temperatures are reached. 

 In the flame of the spirit-lamp or a Bunsen 

 burner, the lines of sodium, as has been said 

 above, are easily produced, but a metal like 

 iron shows nothing. In the blow-pipe flame, 

 the iron shows the dawning of a spectrum 

 by giving series of bands or flutings, a " fluted 

 spectrum," as it has been termed. When the 

 energy of the voltaic arc has been reached by 

 sending a strong current, such as is used by 

 electric tramcars or for lighting, between poles 

 made of iron, then a line spectrum is first 

 reached for iron, and this shows thousands of 

 lines specific for iron at such a temperature. 

 Flame arcs yielding light which would give 

 such spectra are often seen between wheel and 

 rail of a tramcar when vibration of the car 

 or some dirt upon the rails has temporarily 

 broken contact, and an iron arc is formed. 

 A similar copper arc is also frequently seen 

 above when the trolley-wheel leaves the over- 

 head conducting wire, and for a moment a cop- 

 per arc is established. The now well-known 



