10 



MATTER AND ITS MEASUREMENT 



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FIG. 8. 



The Big Dipper and the North Star 

 on September 22, 8 p. m. 



number about 93,000,000 is so large that it means very little to 

 us. We can get a better idea of the distance by saying that it takes 

 over eight minutes (499 seconds) for the sun's light to reach us, al- 

 , though light travels at the rate of about 

 186,000 miles (300,000 kilometers) each 

 second. Or we may say that a train 

 traveling a mile a minute would need 

 about 178 years to get to the sun. Yet 

 the earth's distance from the sun is very 

 small as compared with its distance from 

 the stars. The light of the nearest fixed 

 star requires about 4 years to reach the 

 earth; while the light of Polaris, the 

 "North Star" (Fig. 8), that enters our 

 eyes to-night left the star about 47 years 

 ago. In order to avoid the use of the 

 many figures needed to express such 



enormous distances in miles astronomers use a larger unit for star 

 distances. This unit is the light-year; that is, the distance which 

 light travels in a year. The light-year is about 63,000 times as great 

 as the distance of the earth from the 

 sun, or 63,000X93,000,000 miles. 



12. Weight. Just as we might 

 estimate moderate distances by 

 means of our ' ' sense of distance," 

 or " sense of space," so we might 

 get the weights of many objects 

 by using our li sense of weight." 

 In fact, the experienced cashier 

 and baggageman often develop 

 the sense of weight to a remarkable degree, owing to 

 years of training in the li hefting" of coins and trunks, 

 respectively. However, to get distances accurately we 



FIG. 9. 

 The Chemical Balance. 



