Measurements of Time

The time-measurements most frequently required in practice are determinations of the period of vibration of a needle. To obtain an accurate result some practice in the use of the c eye and ear method' is required. The experiment which follows will serve to illustrate the method and also to call attention to the fact that for accurate work any clock or watch requires careful 'rating', i.e. comparison of its rate of going with some timekeeper, by which the times can be referred to the ultimate standard - the mean solar day. The final reference requires astronomical observations.

Different methods of time measurement will be found in §§21 and 28. The 'method of coincidences' is briefly discussed in §20.