202 



THE POPULAR SCIENCE MONTHLY 



throughout the entire length of the visible path of the meteor. These 

 observations are substantiated by the others more recently made. In Fig. 

 9, the tracks of seventeen trains are shown. The lengths of the paths 

 with respect to altitude are drawn only. The paths of the meteors had 

 different slants and hence differed in length very much more than shown 

 in the drawing. The location of the persistent train is indicated with 



IZO 



no 



100 

 90 



80 



70 



60 



5C 

 W 



30 



20 

 10 



« 



CD 

 CD 



CCl 



I 



¥ 



TEAR WHEN OBSERVED 



U^pfltEna Pomt of Me>f»lTTOcH - O 



Lower End Po>ntof Mrtm Trait + 



EnVue Meleot Train 

 ftirtof Train MCQsurc^- 



1,10 

 IIP 

 100 

 90 



60 



7G 



60 



50 



w 



3 



23 



10 



tZZ. 



sunruc or the earth 



Fig. 9. Chart giving Vertical Projections of the Paths of Seventeen 

 Meteors, showing the altitudes of the trains. In a number of cases the mean altitude 

 of the train has been measured only. 



respect to the length of the entire track or trail, and it is evident from 

 the chart that the production of the long enduring glow has something 

 to do with the altitude of the meteor above the earth. As already 

 stated, the upper and lower limits of the zone in the atmosphere where 

 the trains are formed appear to be usually about sixty and fifty miles 

 respectively from the earth's surface. If the glow is considered to be 

 a phosphorescence of the rarefied air in the meteor's track, the con- 

 clusion that must be drawn, based on laboratory experiments, is that 

 the barometric pressure at these heights is not far from two-tenths of 

 a millimeter of mercury, or, in the neighborhood of from one two-thou- 

 sandth to one four-thousandth of the pressure at the surface of the 

 earth. Any information relating to the density of the atmosphere at 

 great altitudes would be of value, making this part of the research an 

 important one. 



