Sympathetic inks which are developed under the influence of heat only are much easier to use than the foregoing. The liquids which possess such a property are very numerous. Almost every one perhaps knows that if writing be executed on paper with a clean quill pen dipped in onion or turnip juice, it becomes absolutely invisible when dry; and that when the paper is heated the writing at once makes its appearance in characters of a brown color. All albuminoid, mucilaginous, and saccharine vegetable juices make excellent sympathetic inks; we may cite, as among the best, the juices of lemon, orange, apple, and pear. A dilute solution of chloride of copper used for writing is invisible until the paper is heated, when the letters are seen of a beautiful yellow, disappearing again when the heat that developed them is removed. The salts of cobalt, as the acetate, nitrate, sulphate, and chloride, possess a like property. When a dilute solution of these salts is used as an ink, the writing, although invisible when dry, becomes blue when exposed to heat. The addition of chloride of iron, or of a salt of nickel, renders them green, and this opens the way for a very pretty experiment: If a winter landscape be drawn in India ink, and the sky be painted with a wash of cobalt alone, and the branches of the trees be clothed with leaves executed with a mixture of cobalt and nickel, and the snow-clad earth be washed over with the same mixture, a magic transformation at once takes place on the application of heat, the winter landscape changing to a summer scene. There is a well known proprietary article sold in Paris under the name of _"Encre pour les Dames"_ (ink for ladies). Hager, in a recent scientific journal, states that this consists of an aqueous solution of iodide of starch, and is "specially intended for love letters." In four weeks characters written with it disappear, preventing all abuse of letters, and doing away with all documentary evidence of any kind in the hands of the recipient. The signers of bills of exchange who use this ink are of course freed from all obligations in the same length of time. * * * * * NEW WIRE CLOTHING FOR BURRING CYLINDERS. Heretofore two kinds of clothing for cylinders for treating fibrous material have been employed, one consisting of a set of serrated rings cut from sheet steel and secured to the periphery of the cylinder, and the other consisting of flat serrated iron wire. The serrated rings, of necessity, entail a great loss of material in their manufacture, and the iron wire clothing is so soft that it soon wears out or becomes dull, necessitating the reclothing or sharpening of the cylinder. [Illustration: NEW WIRE CLOTHING FOR BURRING CYLINDERS.] Our engraving represents a new form of steel wire clothing for such cylinders, which was recently patented by Mr. Frank P. Pendleton, of Philadelphia, Pa.