Felix Plateau describes in Les Mondes an ingenious process for drawing on paper white lines on a black ground - a method frequently used for astronomical illustrations - by means of which both author and artist are able to judge of the effect of such an illustration before putting it into the hands of the engraver. A piece of thickish paper, as smooth as possible, a little larger than the intended illustration, is heated, by laying it, with proper precautions. against being injured, on the top of a stove, and a piece of bees-wax is rubbed over it until the paper is completely covered with a thin coating. A piece of glass, the size of the paper, is blackened by being held over a candle, and, when thoroughly cooled, it is laid on the waxed paper and rubbed thoroughly with the fingers, the result being that a blackened surface is produced on the paper, on which any design can be traced with a needle for the finer lines, or the back of a steel pen for the thicker ones.