90 H. A. Newton — The Story of Biela's Comet. 



the mind's eye) the meteoroids strewn along the elliptic orbit 

 of the comet for hundreds of millions of miles, forming a stream 

 of unknown breadth, but in the scale of the first figure shown 

 you, about — of an inch in thickness. 



Come back now and stand inside the stream, at its densest 

 part. You in fact see nothing ; but the meteoroids are all about 

 you scattered quite evenly, and distant each from its nearest 

 neighbors 20 or 30 miles. They all travel the same way and 

 with a common motion. 



Once more change your place and look up from the earth's 

 surface. The meteoroids can now be seen, for when they 

 strike the air they burn with intense light, becoming shooting 

 stars. As it is from this position only that we ever see them, 

 note their behavior with more care. A shooting star coming 

 toward you appears only as a bright stationary point in the 

 sky. That point is a marked one in every star shower, and is 

 called the radiant. The meteors to the right and left of the sta- 

 tionary one are, in fact, moving in the common direction, but 

 they seem to move in the sky away from the radiant (fig. 11). 



11. 12. 





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-l N 



In other words, the tracks produced backward will all meet in 

 one point in the sky (fig. 12). This radiant point may be 

 in the horizon, or in the zenith, or at any place between. It 

 will in general rise in the east and set in the west, like the sun 

 or a star, keeping always its fixed place among the stars. 



Need I tell you how much we would like to have some of 

 these bits from the meteoroid streams to handle, to try with 

 the blowpipe and under the microscrope, perhaps thus to learn 

 something of their history? We do have something like this. 

 At times large meteor masses come crashing into the air. They 

 burn with a light bright enough to be seen over several States. 

 Coming down usually a little lower than the shooting stars, 

 most frequently to a height of 25 or 30 miles, they break up 

 with a noise like the firing of heavy artillery, to be heard over 

 several counties. Fragments scattered in every direction fall 

 to the ground over a region ten or twenty miles in extent. I 



