COMMON THINGS TIME. 



near the wire. Again observing the time shown by the clock, 

 again counting the beats he observes, in like manner, the moment 

 at which the eastern edge touches the wire. 



Now let us suppose the times of contact to be as follows : 



Contact of Western limb 

 Contact of Eastern limb 



Transit of sun's centre 



H. 

 12 

 12 



M. 



10 



11 



24 22 



12 11 



As has been already explained, the time of the transit of the 

 -centre of the sun's disc is found by adding together the times of 

 the transits of the eastern and western limbs, and dividing the 

 sum by two. 



It would then appear from this that the time shown by the 

 clock at the moment of apparent noon is eleven minutes and three 

 seconds, and nine-tenths of a second after twelve. 



Let us suppose that the observer then refers to the table of the 

 equation of time for the day of the observation, and finds there 

 that the moment of mean noon was 3 ra 32^ earlier than the 

 apparent noon. To find the time of mean noon, therefore, as 

 shown by the clock, he performs the following arithmetical 

 operation : 



From apparent noon . 

 Subtract the equation of time 



H. M. 



12 11 

 3 



12 



From which it appears that the clock is 7 m Sl^ 5 fast. 



Leaving the clock unaltered, the same observations and calcu- 

 lations are made the following or any succeeding day, and if the 

 clock gives a later hour than 12 h 7 m 31^ 8 for mean noon, its rate 

 is too fast, or it "gains." If it gives an earlier hour, its rate 

 is too slow, or it " loses." Let us suppose, for example, that after 

 the lapse of five days the clock gives 12 h 8 m 25^ s for mean noon, 

 we shall have 



Mean noon sixth day 

 ,, first day . 



Clock gains in five days 



H. M. 

 12 8 

 12 7 



53/5 



The clock therefore gains at the rate of 10-^ seconds per day. 

 The method of correcting the rate is by lengthening the 

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