/toeteors. * 31 



not come within the region of our atmosphere, 

 and when this happens the great velocity at 

 which they travel is the means of their own 

 destruction. They become intensely heated 

 by friction against the atmosphere just as a 

 bullet will when fired from a gun only to a 

 greater extent owing to the greater velocity. 

 They disintegrate into dust which floats in the 

 air for a time, when more or less of it is pre- 

 cipitated upon the surface of the earth. Dis- 

 integrated meteors, or star dust, as they are 

 sometimes called, are often brought down by 

 the rain or snow. Most of the shooting stars 

 that we observe are very small, resembling fire- 

 flies in the sky, but once in a while a very 

 large one is seen moving across the face of the 

 heavens, giving off brilliant scintillations that 

 trail behind the meteor, making a luminous 

 path that is visible for some seconds. These 

 brilliant manifestations are due to one of two 

 causes. Either there is a very large mass of 

 incandescent matter or else they are so much 

 nearer to us than in ordinary cases that they 

 appear larger. It is more likely, however, 

 that it is due to the former cause rather than 

 the latter, from the fact of its apparently slow 

 movement as compared with the smaller shoot- 

 ing stars. It has been determined by observa- 

 tion that the average meteor becomes visible 

 at a point less than 100 miles above the earth's 

 surface. It was found as far back as 1823 that 



