In the case of using the luminous cement upon a wall or ceiling, they sponge or brush the surface over with a solution of paraffine wax and benzoline, or other suitable damp-proofing solution. The uses of a luminous cement are manifold; e.g., for the garden, luminous concrete as edging to garden-paths and carriage-drives; for guides and beacons at the entrance-gates of drives; insides of stables; the base of balustrades, or the entirety of balustrades; for roads, as luminous beacons of corners of dark country lanes, and at the ends of bridges, ends of walls, and curbs of foot-paths; for docks; for edging of piers and wharves; for water-works; for the safety and despatch of night-work by the erection of luminous guides and beacons; and for fire-plug notices on walls; in short, for any place where the light of day will sufficiently excite the phosphorescent property as to render the cement or concrete work luminous by night. The difficulty of sighting rifles in the dark has been ingeniously overcome by the use of luminous paint, and it is thought that the armies of various nations will adopt phosphorescent sights for general use. I have before me as I write, through the courtesy of M. Raphael Dubois of Paris, a fine photograph of a bust of Claude Bernard, taken by the light of numbers of phosphorescent insects (elaters), which shows the possibility of work in this direction. M. Ch. V. Zenger of Paris has made some interesting experiments, and expressed the belief, some time in 1883, that Mount Blanc could be photographed by phosphorescent light emitted, and I understand this has been accomplished. M. Zenger has photographed objects by the light of Balmain’s phosphoric plates. From a personal communication from this scientist, I will quote some things which he has kindly submitted for the author’s use in this volume, referring to this work and the use of Balmain’s liquid phosphorus. As a light, he says, “No doubt there may exist better and more perfect phosphorescent bodies of green, greenish blue, and violet hue, than are at my disposal; and to avoid the use of sulphurets and sulphides, etc., and to obtain as long a phosphorescence as possible, is all I want to reduce stellar photography to the simplest and cheapest apparatus, and make it available to every one.”