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the lamps, being purple rather than red. The reflection is from very

small particles continuous with one another, and in this case the

particles are fully formed water. We get a rainbow, too, if a man

sprinkles fine drops in a room turned to the sun so that the sun is

shining in part of the room and throwing a shadow in the rest. Then if

one man sprinkles in the room, another, standing outside, sees a

rainbow where the sun's rays cease and make the shadow. Its nature and

colour is like that from the oars and its cause is the same, for the

sprinkling hand corresponds to the oar.

That the colours of the rainbow are those we described and how the

other colours come to appear in it will be clear from the following

considerations. We must recognize, as we have said, and lay down:

first, that white colour on a black surface or seen through a black

medium gives red; second, that sight when strained to a distance

becomes weaker and less; third, that black is in a sort the negation

of sight: an object is black because sight fails; so everything at a

distance looks blacker, because sight does not reach it. The theory of

these matters belongs to the account of the senses, which are the

proper subjects of such an inquiry; we need only state about them what

is necessary for us. At all events, that is the reason why distant

objects and objects seen in a mirror look darker and smaller and

smoother, why the reflection of clouds in water is darker than the

clouds themselves. This latter is clearly the case: the reflection

diminishes the sight that reaches them. It makes no difference whether

the change is in the object seen or. in the sight, the result being in

either case the same. The following fact further is worth noticing.

When there is a cloud near the sun and we look at it does not look

coloured at all but white, but when we look at the same cloud in water

it shows a trace of rainbow colouring. Clearly, then, when sight is

reflected it is weakened and, as it makes dark look darker, so it

makes white look less white, changing it and bringing it nearer to

black. When the sight is relatively strong the change is to red; the

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