It was a curious experiment, made by the late Dr. Draper, and used by him as an illustration of the possible permanence of all mental impressions, that if a wafer be placed upon a piece of cold burnished steel, breathed upon, and the wafer then removed, when the steel is again breathed upon, even after a lapse of several days, there will appear upon it a spectral image of the vanished wafer. If so slight a contact between insensible materials produces such lasting results, reasons the Doctor, what must be the effect of visual impressions made upon the sensitive ganglia of the brain? May we not believe that everything which the eye beholds is photographed indelibly upon the mind, to be reproduced if we but look for the talismanic number of the negative? It is a startling suggestion, when we think of it, that our brains must receive unerasable pictures of all that our eyes behold, whether we wish to receive them or not; and one that enjoins us to cast our lines in pleasant places. But whether it be true or not that a single impression makes an indelible mental mark, there is no doubt that a repetition of impressions does; and if we want to keep our soul's picture gallery free from unworthy images we must not go where these are seen.—Christian Union.