456 



GENERAL SCIENCE 



One hour corresponds to a difference of 15. If a place has a differ- 

 ence in time of 6 hours from Greenwich, then there will be a difference 

 of 90 in longitude. 



FIG. 347. In what states of the United States does the compass point directly 

 at the north pole? How many degrees must be allowed for New York City? 

 For San Francisco? 



FIG. 348. 



The difference in time between Greenwich time and that at your 

 home is determined by a clock called a chronometer. Every ship 

 carries one of these clocks which gives the time at Greenwich. By 

 observing the sun through an instrument called a sextant, one is 



