UNIVERSAL TIME. 795 



UNIVERSAL TIME.* 



Br W. H. M. CHRISTIE, F. E. S., 



ASTRONOMER ROYAL. 



CONSIDERING the natural conservatism of mankind in the matter 

 of time-reckoning, it may seem rather a bold thing to propose 

 such a radical change as is involved in the title of my discourse. But, 

 in the course of the hour allotted to me this evening, I hope to bring 

 forward some arguments which may serve to show that the proposal 

 is not by any means so revolutionary as might be imagined at the 

 first blush. 



A great change in the habits of the civilized world has taken place 

 since the old days when the most rapid means of conveyance from 

 place to place was the stage-coach, and minutes were of little impor- 

 tance. Each town or village then naturally kept its own time, which 

 was regulated by the position of the sun in the sky. Sufficient accu- 

 racy for the ordinary purposes of village life could be obtained by 

 means of the rather rude sun-dials which are still to be seen on coun- 

 try churches, and which served to keep the village clock in tolerable 

 agreement with the sun. So long as the members of a community can 

 be considered as stationary, the sun would naturally regulate, though 

 in a rather imperfect way, the hours of labor and of sleep and the 

 times for meals, which constitute the most important epochs in village 

 life. But the sun does not really hold a very despotic sway over ordi- 

 nary life, and his own movements are characterized by sundry irregu- 

 larities to which a well-ordered clock refuses to conform. 



Without entering into detailed explanation of the so-called " equa- 

 tion of time," it will be sufficient here to state that, through the vary- 

 ing velocity of the earth in her orbit, and the inclination of that orbit 

 to the ecliptic, the time of apparent noon as indicated by the sun is at 

 certain times of the year- fast and at other times slow, as compared 

 with twelve o'clock, or noon by the clock. [The clock is supposed to 

 be an ideally perfect clock going uniformly throughout the year, the 

 uniformity of its rate being tested by reference to the fixed stars.] In 

 other words, the solar day, or the interval from one noon to the next 

 by the sun, is at certain seasons of the year shorter than the average, 

 and at others longer, and thus it comes about that, by the accumula- 

 tion of this error of going, the sun is at the beginning of November 

 more than sixteen minutes fast, and by the middle of February four- 

 teen and a half minutes slow, having lost thirty-one minutes, or more 

 than half an hour, in the interval. In passing, it may be mentioned 

 as a result of this that the afternoons in November are about half an 

 hour shorter than the mornings, while in February the mornings are 



* Address delivered at the Royal Institution of Great Britain, March 19, 1SS6. 



