Lecture 8 — Cause of other phenomena appearing at night, and of certain that do not.

Sometimes on a fine night we see a variety of appearances that form in the sky: 'chasms' for instance and 'trenches' and blood-red colors.

These, too, have the same cause. For we have seen that the upper air condenses into an inflammable condition and that the combustion sometimes takes on the appearance of a burning flame, sometimes that of moving torches and stars. So it is not surprising that this same air when condensing should assume a variety of colors. For a weak light shining through a dense air, and the air when it acts as a mirror, will cause all kinds of colors to appear, but especially crimson and purple. For these colors generally appear when fire-color and white are combined by superposition. Thus on a hot day, or through a smoky, medium, the stars when they rise and set look crimson. The light will also create colors by reflection when the mirror is such as to reflect color only and not shape. These appearances do not persist long, because the condensation of the air is transient.

'Chasms' get their appearance of depth from light breaking out of a dark blue or black mass of air. When the process of condensation goes further in such a case we often find 'torches' ejected. When the 'chasm' contracts it presents the appearance of a 'trench'.

In general, white in contrast with black creates a variety of colors; like flame, for instance, through a medium of smoke. But by day the sun obscures them, and, with the exception of crimson, the colors are not seen at night because they are dark.

These then must be taken to be the causes of 'shooting-stars' and the phenomena of combustion and also of the other transient appearances of this kind.

49. After assigning the cause of the conflagrations that are seen being moved in the air, the Philosopher here assigns the cause of certain other things that appear at night. About this he does two things.

First, he enumerates the things whose causes he intends to assign and says that sometimes at night, when it is clear, phantoms, i.e., apparitions, are visible in the heaven: for instance, crevices, i.e., gashes, as though the sky were open, and bothyni, i.e., chasms, as though deep breaches, and also blood-red colors.

50. Second, at these, too, have the same cause (342a36), he assigns the causes of these things. About this he does two things:

first, he gives the cause of their appearance;

second, why many other things occur that are not visible, at in general, white in contrast with black creates a variety of colors (342b18).

About the first he does two things:

first, he assigns the cause of the colors;

second, the cause of the crevices and chasms, at 'chasms' (342b14).

He says therefore first that the causes of these apparitions and of the conflagrations discussed earlier are the same. For since it is plain that the upper air (which he earlier called fuel) is so disposed as to be able to be ignited, so that sometimes a flame appears to burn, and sometimes it is ignited to give the appearance of moving torches and stars, it is not strange (since many varieties of ignitings occur in the air) that the upper air should appear colored with every variety of color.

For there are two ways in which air somewhat thickened comes to represent all varieties of colors: one way is when a feeble light, which is not enough to illuminate fully, shines through smoke or thick vapor; another way is when light is reflected off somewhat thickened air. From these two causes especially, there appears in the air a crimson (342a36) and purple color, i.e., reddish and sub-red—for these colors appear especially when things fiery and white are mixed with black. Such a mixture can occur as a result of the two above-mentioned causes: namely, by "superapposition" (described above as a feeble light shining through something fairly thick—as when the sun and the moon and other stars appear crimson when they rise and set, and as though sub-red when their light is not perfect).

But I say this, if heat is present: because when it is cold, vapors are condensed and obscure the light of rising and setting stars more, so that it cannot get through; but when it is hot, the exhalations are finer and permit the light of the stars to pass through. Likewise, if the stars are seen through smoke, they have this color. This mixture can also be produced by the other cause mentioned: namely, refraction, when the object from which the light is refracted (he here calls this object a mirror), whether it be a water-soaked cloud or something other of the same sort, is of such a nature as to reveal color but not shape. He will explain this, when it is question of the rainbow. Then he explains why these colors quickly disappear and do not last long: it is because the cause of their appearance is rapid, i.e., quickly passes—for air does not maintain a given state very long, and becomes thick or fine very easily.

51. Then when he says, "chasms" (342b14), he assigns the cause of "crevices" and "chasms" and says that when light visible in air is interrupted by something dark, due to thicker vapor than usual, depths and openings seem to exist in the heaven. A sign of this is that, when the vapor which interrupts the light becomes thicker still, fiery torches emerge or fall from these "crevices," as though something hot were ejected by the coldness which thickens the vapor. But when that dark vapor which interrupts the light becomes still more condensed and thick, it causes a greater depth to appear, because the white is overcome by black; when the situation is just the opposite, then only a crevice or opening appears. It is plain, therefore, that both apparitions, i.e., that of colors and that of crevices, have a like cause, namely, black and white mixing together: but the purple or crimson color results from white shining through something black, whereas the crevices and chasms result from something black screening the white.

52. Then when he says, in general, white in contrast with black creates a variety of colors (342b18), he shows that many things of this sort occur but are not visible. And he says that white joined with black produces many varieties of color, as appears with flame in smoke, which produces various colors depending on whether the smoke is thick or fine. But by day the sun's brightness prevents these colors from being seen: at night, however, only red appears, because the other colors, such as green and other darker colors, are on account of their darkness like the color of night.

Finally, he sums up what has been determined and says that these must be taken as the causes of shooting-stars and fire-stars and like apparitions that make hasty appearances (342b21), i.e., that are seen to pass by without lasting very long.