362 GENERAL SCIENCE 



or the Far East, are on sale in cities of the United States 

 at hours in the day earlier than these events are said to have 

 occurred. Telegraphic transmission of news has out-stripped 

 the earth's rate of rotation, and the differences in time of 

 the continents gives ample opportunity for publication of the 

 news apparently "before it happened." To visualize such 

 conditions as these, and to be able concisely to express in 

 detail these relationships of time-keeping over the world, 

 is a worthy test of one's ability to think clearly and surely to 

 conclusions based upon involved data. 



SUMMARY 



The calendar as a system for time-keeping makes use of the periods of 

 rotation and of revolution of the earth the day and the year as un- 

 changing time units. Shorter units are obtained by an arbitrary divi- 

 sion of the average length of solar days into hours, minutes, and seconds. 



Pendulums and springs, by proper adjustment of their lengths, may 

 be made to vibrate at an unvarying rate of once per second, or any 

 other short period desired. By means of wheelwork the number of 

 these vibrations can be shown on a dial as so many hours, minutes, 

 and seconds past noon or past midnight. 



A ready means of remembering the relative times of places east and 

 west of one another is to recall that "east clocks are fast clocks," the 

 noons of places east occurring earlier than at places west of them. 



To travel west with the sun has the effect of lengthening the day of the 

 traveler, so that in going around the world he has had one less number 

 of days in that period of travel than has another person who has re- 

 mained at home. The traveler has "lost a day," and somewhere on 

 his journey westward must drop a day from his calendar. In journey- 

 ing eastward around the earth the traveler's days are shortened as he 

 goes to meet the sun, and as the result he has gained a day in making a 

 journey around the earth. It thus becomes necessary somewhere in 

 the journeying to have in succession two days of the same name, i.e., 

 to set his calendar back a whole day. 



" Standard time" is a system of time-keeping whereby the clock 

 readings throughout a whole section of country are the same regardless 

 of the actual time at these different places as indicated by the sun. 



