"From this simple reflection we now proceed to another, which, but little more complicated, exhibits the appearance much more distinctly. A solid cube of glass, or in its stead a cube composed of several plates, is placed on a black mirror, or held a little inclined above it, at sun-rise or sun-set. The reflection of the sky being now suffered to fall through the cube on the mirror, the appearance above described will appear more distinctly. The reflection of the sky opposite to the sun presents four dark points on a light ground; the two lateral portions of the sky present the contrary appearance, namely, four light points on a dark ground. The space not occupied by the corner points appears in the first case as a white cross, in the other as a black cross, expressions hereafter employed in describing the phenomena. Before sun-rise or after sun-set, in a very subdued light, the white cross appears on the side of the sun also.135
"We thus conclude that the direct reflection