ORIGIN OF LUMINOUS METEOR TRAINS 199 



wrong, was about two miles in thickness and fifteen miles in length. 

 About the same time several persistent trains were seen at Dunmore, 

 Northwest Territory, Canada, one of which remained visible twenty 

 minutes, and several others were reported from the Mount Lowe 

 Observatory, California, by Professor F. L. Larkin. 



The Meteor Train Zone 



It is evident that meteor trains that are observed at night occur at 

 a very definite altitude, and furthermore various facts indicate that the 

 formation of the train is due rather to the state of the earth's atmosphere 

 where the train is formed than to the constitution, size or condition 

 of the meteor itself. Also that the train is a glow phenomenon of the 

 phosphorescent type and probably of electrical origin. 



When meteors penetrate into the atmosphere of the earth they 

 blaze forth at various heights, some even at as great an altitude as 100 

 miles, but the average height at which they appear has been found to be 

 about 80 miles. The usual height at disappearance is about 40 miles. 

 These altitudes are based on many observations. There is strong 

 evidence in favor of the hypothesis that there is a certain density of the 

 air which is favorable for the formation of the persistent train, because 

 the altitude above the surface of the earth at which meteor trains occur 

 when seen at night is usually confined to definite limits between forty- 

 five and sixty-five miles, and the height which appears to be most favor- 

 able for longest visible duration is about fifty-five miles. Thirteen trains 

 carefully observed at two or more stations, the altitudes of which have 

 been determined by triangulation by well known astronomers, give a 

 height of fifty-four miles as the mean altitude of the middle portions of 

 the trains. The region where these self-luminous streaks of meteors 

 occur extending from a little above sixty to a little below fifty miles 

 altitude may well be called the meteor train zone of the atmosphere. 



Trains of meteors which fall in daylight or twilight are not infre- 

 quently seen. They appear as thin smoke trains illuminated by the 

 light of the sun, and according to triangulation observations which are 

 possible only when the train is seen from two stations, they occur as 

 low as twenty-five miles altitude, but seldom above forty miles. They 

 are thus as a rule at a much lower altitude than the trains seen at night, 

 which are usually, if not always, above forty-five miles. This fact would 

 seem to indicate that in the upper levels of the atmosphere the glow 

 does not mainly arise from light reflected from fine meteoric dust, but 

 is a luminosity of the gas in the meteor's track. 



The colors of the meteor trains show a good deal of variation ac- 

 cording to the records of observations of different trains. The colors 

 of trains observed at night include orange-yellow, emerald-green, 

 bluish-green, silver and also white. In numerous cases green trains 

 changed gradually to white, and in one instance from greenish to a 



