24:2 SCIENCE OF COMMON THINGS. 



Velocity of light Why some surfaces are brilliant and others dull. 



With a velocity of one hundred and ninety-two thou- 

 sand miles in a second of time. 



1618 Does all light travel equally fast? 



Yes ; the light of the sun, the light of a candle, or 

 the light from houses, trees, and fields. 



1619 How long a time does it require for light to pass from the sun to 

 the earth f 



Eight minutes and thirteen seconds. 



102 O How much time is required for a ray of light to traverse the 

 space intervening between the nearest fixed stars and the earth f 



More than three years ; and from the farthest nebulae 

 hundreds of years will be required. 



1621 What, therefore, would be the consequence if one oj the remote 

 fixed stars were to-day " blotted from the heavens?" 



Several generations of the earth would pass away 

 before the obliteration could be known to man. 



1622 In wJiat manner do the moon and the planets give light f 



They shine only by means of the surfs light, which 

 is reflected from their surfaces. 



1623 Where does the light of houses, trees, and fields come from? 



The light of the sun (or of some artificial light) is re- 

 flected from their surfaces. 



1624 Why are some surfaces brilliant (like glass and steel) and others 

 dull, like lead ? 



Those surfaces which reflect the most light are the 

 most brilliant / and those which absorb light are dull. 



1625 How does the velocity of light compare with the speed of a loco- 

 motive ? 



Light passes from the sun to the earth in about eight 

 minutes ; a locomotive engine, travelling at the rate 

 of a mile in a minute, would require upwards of one 

 hundred and eighty years to accomplish the same 

 journey. 



1626 How does the light of the full moon compare with that of the sun? 



It is estimated to be three hundred thousand times 

 weaker than sunlight. 



1627 The velocity of light is demonstrated by observations on the 

 satellites of Jupiter. Witt you explain how this can be proved? 



