908 2'j: Ays ACTIONS of the American Institute. 



marked by intense magnetic action on tlie earth, the whole electric 

 system thrilling and qnivering under the solar influence. This 

 condition of excitement was immediately followed by. brilliant dis- 

 plays of auroral light in both the northern and southern hemispheres 

 Hence an intimate relation may be inferred to exist between the 

 aurora, terrestrial magnetism, and the physical condition of the great 

 central luminary of the system. Xeither is the earth the sole reci- 

 pient of this magnetic influence. It must in the same manner extend 

 to every member of the system, and when the aurora is flashing in 

 our sky, it- is a grand and imposing inference that the same wonderful 

 agent is illuminating the skies of our sister planets, throwing a 

 redder glow over the surface of fiery Mars, flaming among the moons 

 'and stars around the huge circumference of Jupiter, beaming with 

 milder light in the moonless night of Venus, or clothing with added 

 lustre the grand sj^stem of Saturn. Its influence must also reach to 

 those strange wanderers, always invested with a romantic charm, 

 wliich visit us at distant intervals, and stretching their fiery tales 

 across our orbits, or threading their eccentric course between them, 

 depart — " on the long travel of a thousand years," 



The most eminent physicists diflered in their views as to the eleva- 

 tion at which the auroral light is suspended above the earth. Arago 

 asserted that to attempt to measure the light of the aurora was as use- 

 less as to attempt to measure the height of the rainbow. Sir John 

 Herschel, whose institutions have the power of prophecy, maintained 

 that precisely the same laws of measurement might be applied to the 

 aurora as to any object raised high above the earth. Finally, it was con- 

 ceded that aurora light is undoubtedly to be ascribed to electric action 

 taking place at a very considerable height where tlie air is very rare. 

 Then followed the question, if something could not be learned by 

 'analyzing the auroral light as to the condition of that part of the 

 atmosphere in which the electric action takes place. 



Spectroscopic analysis was therefore applied to the light of a bril- 

 liant aurora, and tl\e result was most surprising and unexpected. If 

 the aurora were due to particles excited to luminosity by electric 

 action the spectrum would have shown a rainbow-colored streak of 

 light. Instead of this a single streak of colored light appeared. This 

 indicated that the light is due*to the incandescence of some gas 

 'through which the electric discharges in upper air take place. This 

 was to have been anticipated, and a practiced chemist would have 

 immediately detected the nature of the gus from the posistion of the 



