CIVIL TIME. 



however distant they may be one from another, must always 

 point at the same moment to the same honr. Such a common 

 motion may be imparted to them by means of an electric current 

 transmitted along conducting wires, similar to those iised for the 

 electric telegraph. In this way all clocks in all parts of the king- 

 dom could be made to indicate the Greenwich time. 



If this measure should be adopted the civil time will have 

 undergone another change, and instead of being the mean time 

 proper to the place, it will be the mean time at Greenwich. 

 Thus the civil time at Liverpool, for example, would differ from 

 the mean time there by twelve minutes. And as the mean time 

 at certain epochs already differs from the apparent time by more 

 than a quarter of an hour, it will sometimes happen that the civil 

 time will differ from the apparent time by nearly half an hour. 

 Thus the sun may be on the meridian of Liverpool, and conse- 

 quently the real mid-day may take place at about half-past 

 eleven o'clock. 



Such a circumstance, however contradictory and anomalous it 

 may appear when considered astronomically, would, however, be 

 attended with no inconvenience in civil life. 



43. The length of a mean solar or civil day, and the method of 

 denning the moment of its commencement, being well understood, 

 it remains to show how the motion of a timepiece is regulated so 

 as to represent it. 



Let us suppose a clock, the pendulum of which is intended to 

 beat seconds, to be roughly regulated, so that its hour-hand shall 

 make two complete revolutions in a day. This approximation to 

 an exact movement may be easily accomplished by many obvious 

 expedients, one of which would be to set it to twelve o'clock when 

 the sun appears to have attained its greatest altitude. 



The clock, thus approximately regulated, being placed near a 

 transit instrument, such as that already described (26), let the 

 observer, as the sun approaches the meridian, direct the telescope 

 to the point of the meridian over which it is about to pass. When 

 the disc of the sun enters the field of view, and is approaching the 

 wire, N s, fig. 2, let the observer look at the clock, and observe 

 the exact time, and let him count the time from that moment by 

 his ear as he listens to the successive beats of the clock. Con- 

 tinuing thus to count, he will find that the western edge of the 

 sun's disc will touch the wire N s at a certain moment between 

 two successive beats, and by practice he will be able to assign the 

 moment of contact between the beats. As the disc of the sun takes 

 about two minutes to pass across the wire, he will have sufficient 

 time to write down the exact time of the transit of the western 

 edge and to return to the telescope before the eastern edge comes 



137 



