146 THE POPULAR SCIENCE MONTHLY. 



hour-hands only, and the general use of the finer divisions into min- 

 utes and seconds is almost entirely the outgrowth of the requirements 

 of modern civilization. Astronomical time-keeping is not here con- 

 sidered. By the Babylonian system of dividing the day, which was 

 used by the Jews and other Oriental nations, the time between sunrise 

 and sunset was portioned into twelve equal parts at all seasons of the 

 year, the hour varying in length with the season. If this method of 

 division still prevailed, the hours in New York city would vary in 

 length from about forty-six to about seventy-five of our present min- 

 utes. In the Arctic regions the inapplicability of this system to gen- 

 eral use would reach its climax of absurdity. 



The general facts upon which all systems of time-keeping are based 

 are commonly understood, but the details are seldom referred to. 



The most primitive kind of timepiece is a sun-dial. Reduced to 

 its simplest form, a sun-dial consists of a straight pole erected upon a 

 permanently fixed circular plate, the shadow of the pole indicating 

 midday when it coincides with a line drawn due north from the base 

 of the pole, the pole being erected upon a line parallel with the axis 

 of the earth. The other hours of the day are indicated by marks upon 

 the circular plate upon which the shadow of the pole successively falls. 



When the sun-dial was invented can not be stated. It was of very 

 ancient origin, and is mentioned in the thirty-eighth chapter of Isaiah. 

 The clepsydra, or water-clock, and the hour-glass, although very an- 

 cient, must from their nature have been invented subsequent to the 

 sun-dial. But sun-dials, of which there are about a dozen different 

 kinds, although common, were never in such general use as clocks are 

 in modern times, and were philosophical rather than popular instru- 

 ments. The clock was invented about 1379, and the pendulum as a 

 regulating power in 1657. 



The rapid development of the science of horology in the present 

 century has been almost coincident with and in no small degree de- 

 pendent upon the construction and operation of railway and telegraph 

 lines. The needs of these great engines of modern civilization created 

 a general demand for exactness in time reckoning which had never 

 existed before. It was required both for the use of their employes 

 and for the public which patronized their lines. 



A sun-dial being stationary, when properly made and adjusted, ex- 

 hibited solar time correctly, and a watch regulated from the dial by 

 the equation of time would also be correct for that particular spot, but 

 the moment the owner of the watch began to move east or west his 

 time-piece no longer registered correct time, and when he traveled 

 with the speed of a railway -train the error was rapidly exaggerated. 



The necessity for exactness before mentioned, and the impossibility 

 of adhering to local time, early attracted the attention of railway man- 

 agers, and caused them much perplexity and annoyance. With the 

 rapid construction of railway lines, the commingling of the various lo- 



