28 FIRST YEAR COURSE IN GENERAL SCIENCE 



year, but even then the sun is not exactly overhead 

 at any place north of the tropic of Cancer. If it were so, 

 there would be no " shady side of the house" at noon. The 

 sun is nearer the southern horizon at noon in December than 

 at any other time, and in March and September it is half- 

 way between its positions in June and December. (LABO- 

 RATORY MANUAL, Exercise II.) 



19. Latitude and Longitude. We have been accustomed 

 to learn the latitude and longitude of a place from a map in 

 a geography without thought as to how these facts are known. 

 The latitude and longitude of a place were originally deter- 

 mined by observations upon the position of the sun and stars 

 as seen from that place, or as calculated from an observatory 

 whose exact distance and direction from that place were 

 known. 



Sea captains find the latitude and longitude of their 

 vessels by observations made daily, and if for some days 

 neither sun nor stars are visible, a ship may go far out of her 

 course. The United States government employs astrono- 

 mers at the Naval Observatory at Washington to compute 

 the positions of the sun, moon, and many of the stars for 

 some years in advance. Thus navigators sailing on long 

 voyages may be provided with the means of making rapid 

 and accurate calculations from their observations. 



If we could imagine ourselves ignorant of where we are, 

 of the day of the year, and of the hour of the day, we might 

 be able to realize something of what we owe to man's knowl- 

 edge of the heavenly bodies. Calendars and timepieces are 

 made and corrected with reference to the positions of the 

 earth and the sun at certain times. 



At least once every day the correct time, as determined 

 by the position of the sun or some star, is telegraphed from 

 the Naval Observatory to every city in the country. By 

 electric connections, many clocks are thus set right once a 

 day. The calendar, as we call the division of the year into 



