Nevertheless, as presenting us with the first recorded ideas on these questions of the nature and properties of the earth, it deserves attentive study. It is not a system of observations like those of Ptolemy and the Alexandrian School, but an entirely theoretical work. It is founded entirely on logic; but unfortunately, if the premisses are bad, the better the syllogism the more erroneous will be the conclusion; and it is just this which we find here. Thus if he be asked whether the earth turns or the heavens, he will reply that the earth is _evidently_ in repose, and that this is the case not only because we observe it to be so, but because it is a necessity that it should be; because repose is _natural_ to the earth, and it is _naturally_ in equilibrium. This idea of "natural" leads very often astray. He is guided to his idea of what is natural by seeing what is, and then argues that what is, or appears to be, must be, because it is natural--thus arguing in a circle. Another example may be given in his answer to the question, Why must the stars move round the earth? He says it is natural, because a circle is a more perfect line, and must therefore be described by the perfect stars, and a circle is perfect because it has no ends! Unfortunately there are other curves that have no ends; but the circle was considered, without more reason, the most perfect curve, and therefore the planets must move in circles--an idea which had to wait till Kepler's time to be exploded. One more specimen of this style may be quoted, namely, his proof that every part of heaven must be eternally moving, while the earth must be in the centre and at rest. The proof is this. Everything which performs any act has been made for the purpose of that act. Now the work of God is immortality, from which it follows that all that is divine must have an eternal motion. But the heavens have a divine quality, and for this reason they have a spherical shape and move eternally in a circle. Now when a body has a circular motion, one part of it must remain at rest in its place, namely, that which is in the centre; the earth is in the centre--therefore it is at rest. Aristotle says in this work that there are two kinds of simple motion, that in a circle and that in a straight line. The latter belongs to the elements, which either go up or down, and the former to the celestial bodies, whose nature is more divine, and which have never been known to change; and the earth and world must be the only bodies in existence, for if there were another, it must be the contrary to this, and there is no contrary to a circle; and again, if there were any other body, the earth would be attracted towards it, and move, which it does not. Such is the style of argument which was in those days thought conclusive, and which with a little development and inflation of language appeared intensely profound.