CHRONOMETERS. 99 



this for several nights successively (as suppose 

 twenty) ; then if at the end of that time the star 

 vanished as much sooner than it did the first night 

 by the clock, as answers in the time denoted in the 

 table for so many days, the clock goes true, other- 

 wise not. If the difference between the clock and 

 the star be less than the table shows, the clock 

 goes too fast ; if greater, it goes too slow, and 

 must be regulated accordingly, by letting down or 

 raising the ball of the pendulum, by little and by 

 little, turning the screw-nut under the ball, till you 

 find it keeps true equal time. Thus, supposing 

 the star should disappear behind a chimney any 

 night when it is twelve by the clock, and that on 

 the twentieth night afterward the same star should 

 disappear when the time is 41 minutes 22 seconds 

 past ten by the clock, which being subtracted 

 from 12 hours minutes seconds, leaves re- 

 maining 1 hour 18 minutes 38 seconds for the 

 time the star is then faster than the clock : look in 

 the table, and against 20, in the left-hand column, 

 you will find the acceleration of the star to be 

 1 hour 18 minutes 38 seconds, agreeing exactly 

 with what the difference ought to be between the 

 clock and star ; which shows that the clock mea- 

 sures true equal time, and agrees with the mean, 

 solar time, as it ought to do. 



Amongst the most extraordinary pieces of mo- 

 dern clock-work, are those at Strasburgh and 

 Lyons, which are very eminent for the richness of 

 their furniture, and the variety of their motions 

 and figures. In the former a cock claps his wings, 

 and proclaims the hour ; and the angel opens a 

 door, and salutes the Virgin, and the Holy Spirit 

 descends on her, &c. In the latter, two horsemen 

 encounter, and beat the hour on each other j a 



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