nYEXTIETH CENTURY SCIENCE PROBLEMS. 239 



thousands of the heavenly bodies, and in all stages from thin gaseous 

 masses to cold non-luminous solid bodies. 



Kow that we know so much of the past history of the solar system, 

 and in addition that our nearest neighbor is more than 200,000 times 

 the distance to the sun, also that the whole system is itself moving 

 in space at the rate of about 400 millions of miles a year in the 

 direction of the star Vega, we yet need to know whether this motion 

 is a drift or part of an orbit. At present no one knows. The direc- 

 tions and rates of motion of a number of stars have been very well 

 determined, but such measures are not numerous enough to enable us 

 to say whether there is more order in the movements of stars than 

 there is among the molecules of a gas, where molecular collisions are 

 constantly taking place. Such phenomena as that of the new star 

 which suddenly blazed out in Perseus are now explained only by as- 

 suming stellar collisions wherein the masses are so large and have such 

 velocity that impact at once reduces them to incandescent gas. This 

 means the possibility of such disaster to the solar system, but it is a 

 present comfort to know that if we were to collide with our nearest 

 neighbor at present rate, 12 miles a second, it will take nearly 50,000 

 years to reach it. 



We have now about a hundred million stars in sight, and as- 

 tronomers have been surprised that a greater number of the more re- 

 mote ones are not to be seen. The actual number of stars in our 

 universe is much smaller than had been supposed, and instead of there 

 being an infinite number in an infinite space the present outlook is 

 that there is a boundary to the visible universe; but this remains to be 

 determined, and this problem is engaging attention in several of the 

 great observatories. We all want to know what kind of a universe we 

 live in and the series of events that take place in it. In older times 

 there were supposed to be but seven members of the solar system. The 

 nineteenth century discovered more than five hundred. Eros was dis- 

 covered only six or eight years ago, while additional moons to both 

 Jupiter and Saturn were seen for the first time within ten years. It 

 is not probable that all have been discovered. Search is yet being 

 made for other planets. 



Though limited, one can get some idea of the magnitude of the uni- 

 verse when it appears that some of the remote stars are so far away 

 as to require something like a million years for their light to reach us, 

 though light travels at the rate of 186,000 miles a second— a distance 

 so great that it would take trillions of years to reach them at the rate 

 that we now are moving in space, namely about 400 millions of miles 

 a year. Space seems illimitable, time is long, and if matter be inde- 

 structible, yet the solar system as we know it will have gone through 

 all its phases of growth, maturity, old age and death, long enough be- 

 fore the general aspect of the heavens will have been greatly changed 



