22 A NATURALIST IN THE GREAT LAKES REGION 



number. These stars are themselves not fixed but are moving 

 through space with terrific speed. Our sun, carrying the other 

 bodies of the solar system along with it, is swinging along in 

 its orbit at the rate of some twelve miles per second, but 

 neither the size of its orbits nor its center has as yet been 

 determined. 



What a tremendous tangle of pathways is woven by these 

 onrushing suns, their circling planets, and the moons that move 

 about them. The criss-crossing railroads of our country present 

 a simple maze in comparison. What a splendid opportunity for 

 an occasional smash-up if two of the suns or two of the yet more 

 numerous dark bodies should dispute with each other the right 

 of way at some crossing of their pathways. Astronomers tell 

 us that this sort of thing occasionally happens, resulting in the 

 blazing out of a new star as two of the dark bodies rush head- 

 long together, generating thereby enough heat to change their 

 substance into a cloud of incandescent material. 



Even more frequently two bodies will come close enough 

 together as they rush by each other to disrupt each other, each 

 being torn more or less to pieces by opposing forces, the momen- 

 tum of its own precipitate motion in its pathway, and the attrac- 

 tion of the other body. It is from some such wreckage that our 

 solar system is supposed to have originated. The largest 

 remaining fragment or coterie of fragments dominated the rest 

 and became the nucleus of reorganization, the central sun. 

 About it, as a resultant of their original impetus and the force 

 of mutual attraction, the smaller fragments revolved, drawing in 

 turn about them the still smaller ones. 



Our earth began, then, as a knot of dense material in the 

 cloud of fragmented material. By its attraction it drew to 

 itself the smaller bits about it and they moved toward it with 

 increasing momentum, finally smashing down on to its surface. 

 Gradually the earth nucleus grew as it accumulated these tiny 

 revolving bodies, the planetesimals, whose pathways brought 

 them within reach of its quite powerful attraction. 



