Meteorology   

the lower lamp from the flame above. For here too the flame passes

wonderfully quickly and looks like a thing thrown, and not as if one

thing after another caught fire. Or is a 'star' when it 'shoots' a

single body that is thrown? Apparently both cases occur: sometimes

it is like the flame from the lamp and sometimes bodies are

projected by being squeezed out (like fruit stones from one's fingers)

and so are seen to fall into the sea and on the dry land, both by

night and by day when the sky is clear. They are thrown downwards

because the condensation which propels them inclines downwards.

Thunderbolts fall downwards for the same reason: their origin is never

combustion but ejection under pressure, since naturally all heat tends

upwards.

When the phenomenon is formed in the upper region it is due to the

combustion of the exhalation. When it takes place at a lower level

it is due to the ejection of the exhalation by the condensing and

cooling of the moister evaporation: for this latter as it condenses

and inclines downward contracts, and thrusts out the hot element and

causes it to be thrown downwards. The motion is upwards or downwards

or sideways according to the way in which the evaporation lies, and

its disposition in respect of breadth and depth. In most cases the

direction is sideways because two motions are involved, a compulsory

motion downwards and a natural motion upwards, and under these

circumstances an object always moves obliquely. Hence the motion of

'shooting-stars' is generally oblique.

So the material cause of all these phenomena is the exhalation,

the efficient cause sometimes the upper motion, sometimes the

contraction and condensation of the air. Further, all these things

happen below the moon. This is shown by their apparent speed, which is

equal to that of things thrown by us; for it is because they are close

to us, that these latter seem far to exceed in speed the stars, the

sun, and the moon.