Meteorology   

the light is the motion of the constellations and nothing else. For if

it is found in the circle in which there are most constellations and

at that point in the circle at which they are densest and contain

the biggest and the most stars, it is natural to suppose that they are

the true cause of the affection in question. The circle and the

constellations in it may be seen in the diagram. The so-called

'scattered' stars it is not possible to set down in the same way on

the sphere because none of them have an evident permanent position;

but if you look up to the sky the point is clear. For in this circle

alone are the intervals full of these stars: in the other circles

there are obvious gaps. Hence if we accept the cause assigned for

the appearance of comets as plausible we must assume that the same

kind of thing holds good of the milky way. For the fringe which in the

former case is an affection of a single star here forms in the same

way in relation to a whole circle. So if we are to define the milky

way we may call it 'a fringe attaching to the greatest circle, and due

to the matter secreted'. This, as we said before, explains why there

are few comets and why they appear rarely; it is because at each

revolution of the heavens this matter has always been and is always

being separated off and gathered into this region.

We have now explained the phenomena that occur in that part of the

terrestrial world which is continuous with the motions of the heavens,

namely, shooting-stars and the burning flame, comets and the milky

way, these being the chief affections that appear in that region.



9



Let us go on to treat of the region which follows next in order

after this and which immediately surrounds the earth. It is the region

common to water and air, and the processes attending the formation

of water above take place in it. We must consider the principles and

causes of all these phenomena too as before. The efficient and chief