Both M. Boeckh and Gruppe assume the incompatibility of the two meanings; and we find the same assumption in Plutarch's criticisms on the Timæus (Plutarch. Quæst. Platon. p. 1006 C), where he discusses what Plato means by [Greek: o)/rgana chro/nou]; and in what sense the earth as well as the moon can be reckoned as [Greek: o)/rganon chro/nou] (Timæus, p. 41 E, 42 D). Plutarch inquires how it is possible that the earth, if stationary and at rest, can be characterised as "among the instruments of time;" and he explains it by saying that this is true in the same sense as we call a gnomon or sun-dial an instrument of time, because, though itself never moves, it marks the successive movements of the shadow. This explanation might be admissible for the phrase [Greek: o)/rganon chro/nou]; but I cannot think that the immobility of the earth can be made compatible with the attribute which Plato bestows upon it of being [Greek: phu/lax kai\ _dêmiourgo\s_ nukto\s te kai\ ê(me/ras]. The difficulty, however, vanishes when we understand the function ascribed by Plato to the earth as I have endeavoured to elucidate it. The earth not only is not at rest, but cannot be at rest, precisely because it is packed round the solid revolving cosmical axis, and must revolve along with it. The function of the earth, as the first and oldest of intra-kosmic deities, is to uphold and regulate the revolutions of this axis, upon which depend the revolutions of the sidereal sphere or outer shell of the kosmos. It is by virtue of this regulating function (and not by virtue of its rotation) that the earth is the guardian and artificer of night and day. It is not only "an instrument of time," but the most potent and commanding among all instruments of time.