68 Proceedings of the Royal Irish Academy. 



in the clock -rate, when it may be replaced by the 3 or the 9. The 

 ordinary daily correction is simply made by changing one of the 

 cylinders for another. Thus, to take an example — 



Suppose that to-day the clock showed 59 seconds, that yesterday 

 it was correct, then the Table gives + 2. If, then, the cylinder 11-5 

 were on the pendulum, it should be removed, and 13"5 put on instead. 

 It will, however, occasionally happen that the required correction is 

 beyond the reach of the change which could be effected by one 

 cylinder. It would be so in the instance just given, if the cylinder 13"5 

 had been on the shelf, instead of 11 "5. The correction would then 

 re'quire a cylinder of 15*5. In this case the cylinder 6 is removed, 

 and 9 put on instead, and then the cylinder 12-5 seconds is put on. 

 The second cylinder is thus only required for secular corrections, as it 

 were ; the ordinary daily correction is effected in a moment by the ex- 

 tremely simple process of changing one cylinder for another. 



The cylinders are very readily removed, without deranging the 

 pendulum, and the number appropriate to each cylinder is engraved 

 upon it. 



Although this method may seem, in describing it, to be somewhat 

 complicated, yet it works with the greatest facility, and leaves nothing 

 to be desired on the score of precision. 



