NORTHERN LIGHTS— EVE 151 



electric discharge from the masts and rigging of a ship when the 

 earth's voltage differs considerably from that of the air. My verdict 

 for what it is worth, is then, that men cannot possibly hear the 

 Northern Liglits, which can make little or no noise, but they may 

 hear something else not far from them, such as a local brush 

 discharge. 



SPECTROSCOPIC EVIDENCE 



The spectrum of the aurora has been photographed, and most of 

 the lines, or bands rather, are found to be due to nitrogen, which is 

 the major constituent of the atmosphere (about four-fifths) here on 

 earth, and remains the chief constituent at high elevations. The 

 spectrum of the aurora also includes the famous green line which Sir 

 John McLennan investigated so ably, and proved to be due to oxygen 

 in an enhanced or unusual, excited state. He and his coworkers 

 actually produced the green line in his laboratory at Toronto by suit- 

 able stimulation of oxygen with helium, neon, or argon also present. 

 About 1 percent of the air at ground level is argon. All the other 

 rare gases are present in much minuter quantities — neon, krypton, 

 xenon, radon. Hydrogen is so light, and the molecular velocity in 

 consequence so large, that the hydrogen overcomes gravity and passes 

 out of the atmosphere. 



Some of these gases, notably neon, the ingenious Claude has shown 

 us how to collect, to place in tubes at low pressure, and to ionize 

 with high voltage, so that every city is besplangled with artificial 

 auroras, and decorated with an extraordinary variety of colored signs 

 and vivid advertisements. The question is whether we most admire 

 their scientific interest, their intrinsic beauty, or the subtle skill with 

 which they invite or induce the public to buy. It was supposed that 

 some of the rare gases played a part in the rich coloring of auroras, 

 and McLennan suggested that at high altitudes there is more helium 

 than oxygen. On the other hand, experiments by Kaplan indicate 

 that enhanced nitrogen can also stimulate oxygen to emit the light of 

 the green line. Furthermore, the extended researches of Vegard 

 show that the spectra of auroras contain lines or bands of nitrogen 

 and oxygen only. No traces of hydrogen or helium were found. 



THE AURORA AND MAGNETISM 



Everyone today is familiar with a magnetic field, particularly as 

 everyone has lived all his life in a feeble field of that character due to 

 our great magnet the earth. It is not suggested that we know exactly 

 what magnetism is, but then that is true of everything else. The 

 magnetic compass needle, in some form or other, can reveal to us 

 both the direction and intensity of this field at any desired point. 

 Most people also know something of the behavior and properties of 



