122 ANSWERS TO PRACTICAL QUESTIONS 



divisible by 400, was not a leap-year. Many other such dates 

 may be named. 



12. When will a watch and a sun-dial agree ? 



(See Astronomy, p. 265.) 



13. What star will be the Pole Star next after Polaris ? 



(See Astronomy, p. 217.) 



14. Why is the birthday of Washington celebrated on 

 Feb. 22, ivhen he ivas born Feb. 11, 1732 (O. 8.} ? 



(See Astronomy, note, p. 312.) 



15. Does the tide have any effect on the length of the 



day? 



(See Astronomy, notes, pp. 89, 303.) 



16. Will the jBiff Dipper always look as it does now ? 



(See Astronomy, note, p. 217.) 



The following figure, taken from Proctor's Easy Star Les- 

 sons, represents the location of the seven stars comprising the 

 Big Dipper, as they will be seen 100,000 years hence : 



*/? 



17 Hoiv many times docs the earth turn on its axis 

 every year ? 



(See Astronomy, p. 264.) 



18. Does the spectroscope tell us any thing concerning 

 the constitution of the moon, or any of the planets ? 



These bodies shine, in general, by reflected light ; therefore, 

 the light examined comes from the sun. By comparing this re- 

 flected light with solar light, the change produced by the planet's 

 atmosphere may be detected. The lunar spectrum exactly 

 accords with the solar spectrum. The spectra of Venus, Mars, 

 Jupiter, and Saturn contain absorption lines indicating aqueous 

 vapor. Bead Schellen's Spectrum Analysis, p. 333. 



19. When the United States bought Alaska from Rus- 

 sia, the calendar used there was found to be one day ahead 

 of our reckoning. Why was this ? 



