STANDARD TIME IN THE UNITED STATES. 175 



times in advance of it, and sometimes later; so that the moment when 

 the sun was highest at a certain place does not mark a determinate 

 instant unless the day of the year is also given. 



It is necessary to remember this, and to insist somewhat upon it, 

 as the idea that the local noon as determined by clocks and watches 

 is a sort of naturally determined epoch is widely spread, while the 

 fact is that it is an artificial epoch, w^hich can only be fixed by a 

 somewhat difiicult astronomical observation and a subsequent com- 

 putation. The farm-laborer who eats his dinner in the field at the 

 time that shadows cast by the sun point north and south is the 

 victim of his own ignorance, as he sometimes anticipates the noon of 

 watches and clocks by more than a quarter of an hour, and is some- 

 times equally in retard. The improvement of the balance-watch 

 upon the clepsydra or the hour-glass and other early time-keepers 

 caused the change to be made from apparent to mean time, and the 

 increasing requirements of a complex civilization demand more and 

 more attention to the keeping of accurate standard time. One of the 

 most important functions of observatories is the determination of such 

 a standard of time, and if this were their sole function the expense 

 of maintaining them would be fully repaid. 



If the standard time is important to the man of business in mak- 

 ing his appointments and regulating his affairs, to the traveler in pro- 

 viding railways with a correct time by which to govern the move- 

 ments of trains, and in general to every citizen in his daily occupa- 

 tions on land, it is vital to the successful and safe navigation of the 

 ocean. Every ship that sails for a foreign port must before her 

 departure know the correction of her chronometers to Greenwich 

 time (that is, the number of seconds they are fast or slow on that 

 time), and besides this their rate (or the number of seconds they daily 

 gain or lose). Provided with good chronometers and with these data 

 well determined, a ship sails from her port with the power of deter- 

 mining on any day her position on the earth's surface. 



A simple observation of the altitude of the sun at noon gives, by 

 a short computation, her latitude, and a determination of the angular 

 distance of the sun east or west of her meridian gives the local time. 

 The difierence of the local time of the ship and the Greenwich time, 

 as shown by her chronometers, gives her longitude. Latitude and 

 longitude being known, her place on the chart can be put down with 

 but little uncertainty. This is daily done, if possible, on every one 

 of the ships sailing out of New York City, and on the skill of her 

 officers, the goodness of her chronometers, and the accuracy of their 

 rates, depends the safety of her passengers and cargo. To all men of 

 business, then, in their appointments and affairs on shore and in their 

 commercial ventures by sea, the fact that a standard time is easily 

 attainable and perfectly correct is of no slight importance. To 

 travelers, whether by sea or land, it is truly a matter of life and 



