366 GENERAL SCIENCE 



a convenient substitute for a yardstick. This velocity of 

 light is so great that to encircle the earth (25,000 miles) 

 it would require but one-seventh of a second. To reach the 

 earth from the moon (240,000 miles) light requires some- 

 what more than one and one-fourth seconds, and from 

 the sun (93,000,000) somewhat more than eight minutes 

 (499 seconds). It is interesting to compute the number of 

 miles light travels in one year in view of the fact that astrono- 

 mers calculate the distances of the stars as so many "light- 

 years" from the earth. 



From the star believed to be nearest the earth we are 

 told it requires light more than four years to reach the earth; 

 from Sirius the "Dog Star" that is so conspicuous in the 

 southern sky in a winter evening more than eight years ; 

 from the North Star about forty-seven years; and from those 

 stars most distant, and yet visible on photographic plates 

 made by aid of the telescope, perhaps many hundreds of 

 years. When we consider that a star whose light we are 

 still getting that we still "see" may have been blotted out 

 of existence unnumbered years ago, something of the extent 

 of the Universe is borne in upon the human mind. 



The number of the stars, while not at all a " countless 

 multitude," is nevertheless so great as to cause amazement 

 when we think of them as light-giving bodies like our sun. 

 The number visible to an observer with the naked eye only 

 at any one time and place is perhaps less than .two thousand, 

 or about five thousand in the whole heavens since many just 

 above the horizon are not readily seen. But the number 

 of stars that may be counted on photographic plates of the 

 whole heavens as made by use of the largest telescopes is 

 perhaps several hundred millions. In an exercise of the 

 imagination based upon such facts as these, and that is at 

 all times in accord with facts, there is developed the noblest 



