kő ." LIGHT AND WATER surface of the candlestick is visible, whereas, looking directly at the object, it is out of sight. Anyone looking from E would get a view of the candlestick and its image very similar to that drawn in the figure. The lines ADE, BFE and CGE represent the paths of the rays from A, B and C respectively, which reach the eye after reflexion at the surface of the mirror. And if the straight lines BF, AD and CG are produced downwards they will be found all to meet at a point e, as far beneath the glass in a vertical line as the eye is above it, so that the view of the image seen from E is the inversion of the view of the object that we should get if we were to remove the mirror and look at it from e. It is necessary to note this difference, because the word “ reflexion” is used to denote ¢he observer's view” of the image, and not the image itself. The image always remains the same, being, as we have said, the exact inversion of the object; but the reflexion, or view we get of it, varies with our position. In considering the reflexions seen in a sheet of water we will assume in the first place that its surface is perfectly smooth and unruffled. Reflexion takes place therefore exactly as in the case of the plane mirror." " The line OD, produced both ways, marks the intersection of the plane of incidence of the ray AD with the surface of the mirror. For the sake of simplicity in the figure, the points B and C are chosen in this same plane, so that F and G also lie on the same line OD produced. This line bisects the vertical Ee in L. " Or, projection of the image on to the picture plane. " For the present we ignore the fact that the reflective power water is different for light at different angles of incidence. This fact is, however, taken into account in the third chapter.