Atmosphere we have already alluded to in previous chapters. We saw how Vermeer filled the scene of his picture with lighted air; and, in discussing color, we talked of it first as light, and then went on to study how the light which is in the air affects the light which is reflected from all objects that are visible. We found that colors differ from one another in the quantity of light they contain: in what artists call their values; the value of red, for example, being different from the value of blue or green. Also we found that each single color may have variations of value, according to the quantity and direction of the light which falls upon it.