ORIGIN OF LUMINOUS METEOR TRAINS 191 



THE ORIGIN OF LUMINOUS METEOR TRAINS 



By Db. C. C. TROWBRIDGE 



COLUMBIA UNIVEESITY 



THE nature of the luminous cloud occasionally left glowing in the 

 wake of large meteors and called the " persistent " streak or train 

 has long been regarded as a mystery by astronomers. Many of these 

 trains have been observed which have remained visible to the naked 

 eye for quite as long as fifteen or thirty minutes after the disappear- 

 ance of the burning metorite itself. In numerous instances trains have 

 lasted for more than one hour, floating in the cold upper atmosphere, a 

 luminous mist-like cloud projected against the dark night sky. 



Meteors are usually visible but for a few seconds in their rapid flight 

 through the upper regions of the atmosphere at a velocity of from 

 twenty to thirty or more miles a second. Their track is almost always 

 marked by a bright streak of fast-fading luminosity which also dis- 

 appears from view in a second or two. Occasionally, however, the streak 

 remains for many minutes brightly glowing, continually expanding in 

 size, and drifting with the moving atmosphere. This is the phenom- 

 enon which has been called the " persistent train." 



Meteors which leave these trains are a very small proportion of the 

 total number that are seen, yet authentic and definite facts concerning 

 the trains have been recorded at various astronomical observatories in 

 all parts of the world, hence the chief characteristics of this remarkable 

 phenomenon are known. 



A serious study of the subject has been made only recently, but it is 

 now recognized as being of considerable importance because it teaches 

 important facts concerning the upper atmosphere. 1 Most of the obser- 

 vations of meteor trains which from time to time have been made by 

 different astronomers have been incidental in the course of the usual 

 investigations of the heavens. Perhaps the best way to show the extraor- 

 dinary features of the self-luminous meteor train is by drawings of a 

 bright and long-enduring train carefully observed in England many 

 years ago. The drawing marked A in the first illustration is a sketch 

 made by one of the observers of the train as it appeared only a few seconds 

 after the meteor nucleus had disappeared. This train, which was seen 

 by many observers in the vicinity of both Sidmouth and Cardiff in 

 England at the time of the great meteor shower of 1866, was formed 



1 A grant has been made by the National Academy of Sciences from the 

 J. Lawrence Smith Fund to the author of the present article to enable him to 

 extend his researches on meteor train phenomena. 



