Treatises on meteorology have not, up to the present day, classified with sufficient regularity the divers optical phenomena of the air. Some of these phenomena have, however, been seen but rarely, and have not been sufficiently studied to admit of their classification. We have examined the common phenomenon of the rainbow and we have seen that it is due to the refraction and reflection of light on drops of water, and that it is seen upon the opposite side of the sky to the sun in day-time, or the moon at night. We are now about to consider an order of phenomena which are of rarer occurrence, but which have this property in common with the rainbow, viz., that they take place also upon the side of the sky opposite to the sun. These different optical effects are classed together under the name of _anthelia_ (from Greek, opposite to, and Greek, the sun). The optical phenomena which occur on the same side as, or around the sun, such as halos, parhelia, etc., will be dealt with later on. Before coming to the anthelia, properly so called, or to the colored rings which appear around a shadow, it is as well first to note the effects produced on the clouds and mists that are facing the sun when it rises or sets. Upon high mountains, the shadow of the mountain is often seen thrown either upon the surface of the lower mists or upon the neighboring mountains, and projected opposite to the sun almost horizontally. I once saw the shadow of the Righi very distinctly traced upon Mount Pilate, which is situated to the west of the Righi, on the other side of the Lake of Lucerne. This phenomenon occurs a few minutes after sunrise, and the triangular form of Righi is delineated in a shape very easy to recognize.