As well as the sun and the fixed stars the moon appears in the heavens. It does not entirely vanish before the sunlight like the fixed stars, in the night-time its light eclipses that of the smaller stars. Its shape, the strength of its light, and the time of its appearance vary quite perceptibly from day to day. As long as the human race has existed, man’s attention must have been drawn to the moon. The course of the moon, thanks to the rapid revolution of the planet round the earth, forms a shorter unit, which steps in between day and year. The shorter interval of time defined by it, unlike the too lengthy period of the year, is easily kept in mind and taken in at a glance. This unit has further its peculiar characteristics. In the first place it has nothing to do with the natural phases conditioned by the course of the sun: it is in fact incommensurable with the seasons. In the second place it immediately obtrudes itself into notice as a unit. The time-reckoning according to the moon is in its nature continuous. One moon follows another with a short interruption, to which at first little attention is paid: for compared with the 27-28 days in which the moon can be seen in the sky the 1-2 days in which it is invisible are little noticed. The phases of the moon represent a gradual waxing and waning, a continuous development. The principle of continuous time-reckoning is therefore suggested by the moon, in opposition to the time-indications from natural phases and from the stars. The observation of the moon is often said to be the oldest form of time-reckoning. This statement involves a certain danger, viz. the overlooking of the fact that the time-indications from natural phases and from the stars--as I hope has been shewn above--are just as primitive and must be just as old. But if by time-reckoning the continuous principle and measure of time are implied the statement is in that sense true. The moon is indeed the first chronometer, and this fact is due to the nature of its concrete appearance, which draws attention to the duration, and not to the point, of time. And this, as always, is the starting-point: practically everywhere the month as a unit of enumeration or a measure is denoted by the same word as the moon. The linguistic distinction between ‘moon’ and ‘month’ only follows at a stage which primitive peoples still living have not yet reached. All peoples know the moon and use it for time-reckoning. Of the S. American Indians, who observe the stars so well, it is stated that the month is everywhere the natural division of time[623].