§3.22 περὶ δὲ ἅλω καὶ ἴριδος, τὶ τε ἑκάτερον καὶ διὰ τίνʼ αἰτίαν γίγνεται, λέγωμεν, καὶ περὶ παρηλίων καὶ ῤάβδων·
2 Let us discuss halos and rainbows, what each of them is and for what cause they occur, and also parhelia and rods; for all these occur because of the same causes as one another.
καὶ γὰρ ταῦτα γίγνεται πάντα διὰ τὰς αὐτὰς αἰτίας ἀλλήλοις. πρῶτον δὲ δεῖ λαβεῖν τὰ πάθη καὶ τὰ συμβαίνοντα περὶ ἕκαστον αὐτῶν.
First, we must grasp the phenomena and what happens concerning each of them.
τῆς μὲν οὖν ἅλω φαίνεται πολλάκις κύκλος ὅλος, καὶ γίγνεται περὶ ἥλιον καὶ σελήνην καὶ περὶ τὰ λαμπρὰ τῶν ἄστρων, ἔτι δʼ οὐδὲν ἧττον νυκτὸς ἢ ἡμέρας καὶ περὶ μεσημβρίαν ἢ δείλην· ἔωθεν δʼ ἐλαττονάκις καὶ περὶ δύσιν.
Now, of the halo, a complete circle is often seen, and it occurs around the sun and the moon, and around the bright stars, and moreover, no less by night than by day, and around noon or evening; but from dawn and near sunset, less frequently.
τῆς δʼ ἴριδος οὐδέποτε γίγνεται κύκλος οὐδὲ μεῖζον ἡμικυκλίου τμῆμα· καὶ δύνοντος μὲν καὶ ἀνατέλλοντος ἐλαχίστου μὲν κύκλου, μεγίστη δʼ ἡ ἁψίς, αἰρομένου δὲ μᾶλλον κύκλου μὲν μείζονος, ἐλάττων δʼ ἡ ἁψίς· καὶ μετὰ μὲν τὴν μετοπωρινὴν ἰσημερίαν, ἐν ταῖς βραχυτέραις ἡμέραις, πᾶσαν ὥραν γίγνεται τῆς ἡμέρας, ἐν δὲ ταῖς θεριναῖς οὐ γίγνεται περὶ μεσημβρίαν.
But of the rainbow, a circle never occurs, nor any segment larger than a semicircle; and when the sun is setting or rising, the circle is smallest, but the bow is largest, whereas when it is raised higher, the circle is larger, but the bow is smaller; and after the autumnal equinox, in the shorter days, it occurs at any hour of the day, but in the summer days, it does not occur around noon.
οὐδὲ δὴ δυοῖν πλείους ἴριδες οὐ γίγνονται ἅμα.
Nor indeed do more than two rainbows ever occur at the same time.
τούτων δὲ τρίχρως μὲν ἐκατέρα, καὶ τὰ χρώματα ταὐτὰ καὶ ἴσα τὸν ἀριθμὸν ἔχουσιν ἀλλήλαις, ἀμυδρότερα δʼ ἐν τῇ ἐκτὸς καὶ ἐξ ἐναντίας κείμενα κατὰ τὴν θέσιν· ἡ μὲν γὰρ ἐντὸς τὴν πρώτην ἔχει περιφέρειαν τὴν μεγίστην φοινικίαν, ἡ δʼ ἔξωθεν τὴν ἐλαχίστην μὲν ἐγγύτατα δὲ πρὸς ταύτην, καὶ τὰς ἄλλας ἀνάλογον.
Each of these consists of three colors, and they have the same colors and equal in number to each other, but they are dimmer in the outer one, and positioned opposite in their arrangement; for the inner one has its first and largest circumference red, while the outer one has its smallest circumference closest to this inner one, and the others analogously.
ἔστι δὲ τὰ χρώμματα ταῦτα ἅπερ μόνα σχεδὸν οὐ δύνανται ποιεῖν οἱ γραφεῖς· ἔνια γὰρ αὐτοὶ κεραννύουσι, τὸ δὲ φοινικοῦν καὶ πράσινον καὶ ἁλουργὸν οὐ γίγνεται κεραννύμενον· ἡ δὲ ἶρις ταῦτʼ ἔχει τὰ χρώματα.
And these colors are almost the only ones which painters cannot make; for they themselves mix some colors, but red, green, and purple do not come from mixing, and the rainbow has these colors.
τὸ δὲ μεταξὺ τοῦ φοινικοῦ καὶ πρασίνου φαίνεται πολλάκις ξανθόν.
But the space between the red and the green often appears yellow.
παρήλιοι δὲ καὶ ῥάβδοι γίγνονται ἐκ πλαγίας αἰεὶ καὶ οὔτʼ ἄνωθεν οὔτε πρὸς τῆς γῆς οὔτʼ ἐξ ἐναντίας, οὐδὲ δὴ νύκτωρ, ἀλλʼ ἀεὶ περὶ τὸν ἥλιον, ἔτι δὲ ἢ αἰρομένου ἢ καταφερομένου· τὰ πλεῖστα δὲ πρὸς δυσμάς· μεσουρανοῦντος δὲ σπάνιον εἴ τι γέγονεν, οἶον ἐν βοσπόρῳ ποτὲ συνέπεσε· διʼ ὅλης γὰρ τῆς ἡμέρας συνανασχόντες δύο παρήλιοι διετέλεσαν μέχρι δυσμῶν.
And parhelia and rods always occur from the side, and neither from above nor toward the earth nor from the opposite side, nor indeed by night, but always around the sun, and moreover either as it is rising or setting; and most of them toward the west; but when it is in mid-heaven, it is rare if anything has occurred, as once happened in the Bosporus; for rising together throughout the whole day, two parhelia continued until sunset.
τὰ μὲν οὖν περὶ ἕκαστον αὐτῶν συμβαίνοντα ταῦτʼ ἐστίν· τὸ δʼ αἴτιον τούτων ἀπάντων ταὐτὸ· πάντα γὰρ ἀνάκλασις ταῦτʼ ἐστί, διαφέρουσι δὲ τοῖς τρόποις καὶ ἀφʼ ὧν, καὶ ὡς συμβαίνει γίγνεσθαι τὴν ἀνάκλασιν πρὸς τὸν ἥλιον ἢ πρὸς ἄλλο τι τῶν λαμπρῶν.
The things, then, that happen concerning each of them are these; and the cause of all these is the same; for all these are reflections, but they differ in their manners and from what they reflect, and how the reflection happens to occur toward the sun or toward some other of the bright objects.
καὶ μεθʼ ἡμέραν μὲν ἶρις γίγνεται, νύκτωρ δʼ ἀπὸ σελήνης, ὡς μὲν οἱ ἀρχαῖοι ᾤοντο, οὐκ ἐγίγνετο τοῦτο δʼ ἔπαθον διὰ τὸ σπάνιον·
And by day, indeed, the rainbow occurs, but by night from the moon, which, as the ancients thought, did not occur.
ἐλάνθανε γὰρ αὐτούς·
But they suffered this because of its rarity; for it escaped their notice.
γίγνεται μὲν γάρ, ὀλιγάκις δὲ γίγνεται.
For it does occur, but it occurs rarely.
τὸ δʼ αἴτιον ὅτι τʼ ἐν τῷ σκότει λανθάνει τὰ χρώματα, καὶ ἄλλα πολλὰ δεῖ συμπεσεῖν, καὶ ταῦτα πάντα ἐν ἡμέρᾳ μιῇ τοῦ μηνός· ἐν τῇ πανσελήνῳ γὰρ γενέσθαι ἀνάγκη τὸ μέλλον ἔσεσθαι, καὶ τότε ἀνατελλούσης ἢ δυνούσης· διόπερ ἐν ἔτεσιν ὑπὲρ τὰ πεντήκοντα δὶς ἐνετύχομεν μόνον.
And the cause is both that in the darkness the colors escape notice, and many other things must coincide, and all these on a single day of the month; for it is necessary for it to happen during the full moon, and then as it is rising or setting; wherefore in over fifty years we have met with it only twice.
ὅτι μὲν οὖν ἡ ὄψις ἀνακλᾶται, ὥσπερ καὶ ἀφʼ ὕδατος, οὕτω καὶ ἀπὸ ἀέρος καὶ πάντων τῶν ἐχόντων τὴν ἐπιφάνειαν λείαν, ἐκ τῶν περὶ τὴν ὄψιν δεικνυμένων δεῖ λαμβάνειν τὴν πίστιν, καὶ διότι τῶν ἐνόπτρων ἐν ἐνίοις μὲν καὶ τὰ σχήματα ἐμφαίνεται, ἐν ἐνίοις δὲ τὰ χρώματα μόνον·
That indeed our vision is reflected, just as from water, so also from air and from all things that have a smooth surface, one must grasp the proof from what is demonstrated concerning vision, and also because in some mirrors even the shapes are reflected, but in some, the colors only.
τοιαῦτα δʼ ἐστὶν ὅσα μικρὰ τῶν ἐνόπτρων, καὶ μηδεμίαν αἰσθητὴν ἔχει διαίρεσιν· ἐν γὰρ τούτοις τὸ μὲν σχῆμα ἀδύνατον ἐμφαίνεσθαι (δόξει γὰρ εἶναι διαιρετόν· πᾶν γὰρ σχῆμα ἅμα δοκεῖ σχῆμά τʼ εἶναι καὶ διαίρεσιν ἔχειν), ἐπεὶ δʼ ἐμφαίνεσθαί τι ἀναγκαῖον, τοῦτο δὲ ἀδύνατον, λείπεται τὸ χρῶμα μόνον ἐμφαίνεσθαι.
Such are those of the mirrors that are small and have no sensible division; for in these, it is impossible for the shape to be reflected (for it will seem to be divisible; for every shape seems both to be a shape and to have division), and since it is necessary that something be reflected, but this is impossible, it remains that the color alone is reflected.
τὸ δὲ χρῶμα ὁτὲ μὲν λαμπρὸν φαίνεται τῶν λαμπρῶν, ὁτὲ δέ, ἢ τῷ μείγνυσθαι τῷ τοῦ ἐνόπτρου ἢ διὰ τὴν ἀσθένειαν τῆς ὄψεως, ἄλλου χρώματος ἐμποιεῖ φαντασίαν.
And the color sometimes appears bright from bright things, but sometimes, either by being mixed with that of the mirror or because of the weakness of vision, it produces the appearance of another color.
ἔστω δὲ περὶ τούτων ἡμῖν τεθεωρημένον ἐν τοῖς περὶ τὰς αἰσθήσεις δεικνυμένοις· διὸ τὰ μὲν λέγωμεν, τοῖς δ᾿ ὡς ὑπάρχουσι χρησώμεθα αὐτῶν.
Let these matters be assumed to have been investigated by us in what is demonstrated concerning the senses; therefore, let us state some things, and use others of them as already existing.