go8 Handbook of Nature-Study 



strike against us; but the physicists have found that it does push, and by 

 pushing against the particles of the gas of comets it sends them out into a 

 streamer away from the sun, just as the heat pushes out a flaring cloud of 

 steam from the spout of a teakettle. 



Another thing we know about comets is that they are not able to hold 

 together, but break into pieces; and these pieces become cold out in space 

 and condense and harden into lumps of metallic stone; and these lumps, 

 each one whirling, follows the same track that the comet followed. If a 

 comet should break into many pieces it would make a whole flock of these 

 lumps all going in the same direction and in the same path about the sun. 



Since comets are moving around the sun in every direction, it is possible 

 that the earth may sometime meet one; and if this proves to be a "head on 

 collision" there are those who prophesy that there will be no people left to 

 tell the story ; but the tails of comets are so thin and ethereal that our earth 

 actually passed through one once, and no one but the astronomers knew 

 anything about it. 



SHOOTING STARS 



When we look up during an evening walk and see a star falling through 

 space, sometimes leaving a track of light behind it, we wonder which of the 

 beautiful stars of the heavens has fallen. But astronomers tell us that no 

 real star ever fell, but that what we saw was a lump of the matter of which 

 worlds and comets are made ; and it was following its own swift path around 

 the sun, when by chance it crossed our earth's path, and was drawn toward 

 us by that mysterious power called gravitation, which makes us fall down 

 if we lose our balance, and which also made this bit of world-stuff fall to 

 earth when it came so near us that its balance was disturbed. Although 

 this shooting star was just a dark, cold lump of metal, too small for us to see, 

 yet it was moving so swiftly along its path around the sun that the friction 

 caused by its passing through our air, lighted it and burned it up, just as a 

 match scratched on sandpaper lights and burns ; as soon as it blazed we saw 

 it and said, "There is a shooting star!" Sometimes the lump is so big that 

 it does not have time to burn up while passing through the hundred miles or 

 more of our atmosphere, and what is left of it strikes the earth usually with 

 such force as to bury itself deep in the soil. Such lumps are called "meteor- 

 oids" before they fall and "meteors" while plunging white-hot through the 

 air, but when they reach our earth we call what is left of them "meteorites." 

 There are, in museums, many meteorites of this so-called stone, which is 

 largely iron. Chemists find no new metals or elements in these strangers 

 from space, but they do find new kinds of chemical partnerships and com- 

 binations. Some of these meteorites weigh hundreds of pounds, one in the 

 Yale Museum weighing 1635 pounds. It surely would not be safe for a 

 person to be on the spot where and when one of these meteorites strikes the 

 earth; but there are so few of the meteors large enough to last until they 

 become meteorites, that we may safely continue to enjoy the sight of shoot- 

 ing stars. If it were not for the air that wraps our globe, like a great, kindly 

 blanket, and by its friction sets fire to the meteors and destroys them, no 

 one could live on this earth because we all should be pelted to death. Prof. 

 Newton estimated that every twenty-four hours our world meets seven 

 millions of these shooting stars, some of them no larger than shot and others 

 weighing tons. 



