THE HOUES. 



notation and terminology, should not have been applied to the 

 counting of time. When the spirit of innovation was in the 

 ascendant in France in 1793, such an attempt was made, the day 

 being divided into ten hours, the hour into an hundred minutes, 

 and the minute into an hundred seconds. The power of custom, 

 however, prevailed over even the domination of terrorism and the 

 project signally failed. 



11. The hours into which the day was resolved were generally 

 intended to be equal, each being the twenty-fourth part of the 

 entire interval called a day. Nevertheless, there were some 

 exceptions to this. Thus, at a certain epoch in Greece, the 

 interval between sunrise and sunset was divided into twelve 

 equal parts called hours of the day, and the other interval, be- 

 tween sunset and sunrise, was also divided into twelve equal 

 parts, called hours of the night. It is evident that the diurnal 

 hours were equal to the nocturnal hours only at the equinoxes, 

 and that from the spring to the autumnal equinox the diurnal 

 were longer than the nocturnal hours, and from the autumnal to 

 the spring equinox the nocturnal were longer than the diurnal 

 hours. The hours, both diurnal and nocturnal, were also subject 

 to continual variation of length. From the first day of winter, 

 or the shortest day, to the first day of summer, or the longest day, 

 the diurnal hours constantly increased, and the nocturnal hours 

 constantly decreased in length ; and from the first day of summer 

 to the first day of winter, the nocturnal hours constantly increased, 

 while the diurnal hours constantly diminished. 



Such a system could not be properly denominated chronometric 

 at all, since the interval of time called an hour was different at 

 different seasons. 



12. Defective as such a method of counting time must have 

 been for the purposes of common life, it was utterly inadmissible 

 for any scientific investigations ; and Ptolemy, in his astronomical 

 observations, was always obliged to transform the vulgar hours 

 into equinoxial hours ; so called, no doubt, because it was only at 

 the equinoxes that the vulgar diurnal were equal to the noc- 

 turnal hours. 



How imperfect the art of measuring time was in that age, may 

 be imagined when it is stated that, in the observations of Ptolemy, 

 the time of astronomical phenomena is never indicated nearer the 

 truth than a quarter of an hour. At present it is determined in 

 good observations to less than the tenth of a second. 



13. For chronometric purposes, it is not enough to fix the value 

 of the standard unit of time. It is necessary also to establish a 

 convention as to the moment at which each successive unit com- 

 mences, and the preceding one terminates. In a word, a point of 



