A. Because the pupil of their eyes is much dilated by the dark, and cannot collect from the window sufficient rays to enable them to see into the room.
Q. Why do we often see the fire reflected in our parlour window in winter time?
A. Because glass is a good reflector; and the rays of the fire (striking against the window-glass) are reflected back into the room again.
Q. Why do we often see the shadow of our candles in the window, while we are sitting in our parlour?
A. Because the rays of the candle (striking against the glass) are reflected back into the room: and the darker the night, the clearer the reflection.
Q. Why is this reflection more clear, if the external air be dark?
A. Because the reflection is not then eclipsed by the brighter rays of the sun striking on the other side of the window.
Q. Why is the shadow of an object (thrown on the wall) larger and larger, the closer any object be held to the candle?
A. Because the rays of light diverge (from the flame of a candle) in straight lines, like lines drawn from the centre of a circle.