INTRODUCTION. XXII! Nature or Art? An unreasonable prejudice prevails, to some extent, against all slides not photographed from nature. When there is a choice, as, for example, between a photograph of the Egyptian Pyramids and an artist’s representation, as roughly shown,, page 113 of the Manual, the sun picture surely has the advantage ; yet something can be said, even in this case, for the artist, who gathers the details of many chance observations into one view, and groups the camels and Arabs into an artistic pose more picturesque than would come within the range of a photographer’s average luck. Historic and art pictures, and scientific illustrations, which have been wrought out by the best skill and learn¬ ing of the present and the past, can, for the most part, only be copied into slides from these works of art. Strong or Faint? It is a mistake to suppose that pictures intended for the Sciopticon should be selected with special reference to the light used. The proper density for the Sciopticon llame illumination differs little, if any, from what is best for the lime light proportionally enlarged. Dense pictures fogged in the high lights, may be shown a little, by lime light, and the glaring defects of coarse pictures may show less by oil light, but neither class is worthy of being recommended. The class of customers most anxious to secure clear, bright pictures, are professional exhibitors with a lime light. The Bad and the Good. It is matter for regret, that with our present facilities for producing good slides of every class, so many bad oues