The return of the moon in conjunction with the sun, was observed to occur at regular intervals of twenty-nine days, twelve hours, and some minutes.

This interval is called the _lunar month_, which for a long time was regarded as the radical unit in the admeasurement of time." "But the year is now the unit, is it not ?" "Yes, in course of time the moon, in this respect, gave place to the sun.

It was observed that the earth, in performing her revolution round the sun, always arrived at the same point of her orbit at the end of three hundred and sixty-five days, five hours, fifty-eight minutes, and forty-five seconds." "Does the earth invariably pass the same point at that interval ?" "Yes, invariably; and the interval in question is termed the solar year." "After all," remarked Jack, "the perseverance of the earth is very much to be admired.

It goes on eternally, always performing the same journey, never deviates from its path, and is never a minute too late." "If the earth had performed her annual voyage in a certain number of entire days, the solar year would have been an exact unit of time; but the odd fraction defied all our systems of calculation.

Originally, we reckoned the year to consist of three hundred and sixty-five days." "And left the fraction to shift for itself!" "Yes, but the consequence was, that the civil year was always nearly a quarter of a day behind; so that at the end of a hundred and twenty-one years the civil year had become an entire month behind.