ABOUT THE STARS 221 



One may sometimes see on the coast or in some 

 marshland a "pile-driver" at work. At a quarter of a 

 mile distance you can see the great weight hoisted up by 

 cranks and chains above the " pile," which stands upright 

 but not yet driven very far into the ground. You see the 

 weight let go ; it drops vertically on to the pile, and you 

 watch it rising some two or three feet on its return journey 

 upwards, when suddenly you hear the sound of a sharp 

 blow, and only after an effort realise that the sound was 

 made more than a second ago, and that the workmen 

 have had time to raise the weight 3 ft. before the sound 

 travelled to you. Sound travels less than a quarter of 

 a mile in a second. Light also takes time to travel, but 

 it advances ever so much more quickly than sound, 

 namely, 186,000 miles (and a bit more) in a second. It 

 is, therefore, easy to calculate the number of miles 

 traversed by light in a minute or in a year. There are 

 thirty million seconds in a year. The light of the sun 

 takes eight minutes to reach the earth, so, instead of 

 stating the number of miles of this distance, we may say 

 that the sun is eight "light-minutes" distant from the 

 earth (about 89,000,000 miles). This is an enormous 

 figure. The sun and his planets may be represented 

 proportionately by a golden ball a foot in diameter, and 

 a number of little spheres varying in size from that of a 

 dried pea to a boy's marble, placed at distances from the 

 golden ball varying from 50 ft. to 200 ft. Such a model 

 is shown in the Museum of Practical Geology in Jermyn 

 Street, London. Minute and scattered far apart as the 

 planets of the solar system appear when thus represented, 

 yet the solar system is a compact little group when we 

 come to consider the distance from it of the other suns 

 the "fixed stars," which exist literally in millions beyond 

 it. The nearest of these stars (its name is Alpha Centauri) 

 is no less than three light-years distant from us. A light- 



