When the cylinders, F, occupy the position represented in the engraving by unbroken lines, the flat plate, O, is simply submitted to pressure between the cylinders, D and P, the cylinders, F F, then merely acting as guides. But when, while the plate is being thus flattened between the principal cylinders, the accessory cylinders are caused to rise, the plate is curved as shown by the dotted lines, O' O'. To obtain a uniformity in the position of the two cylinders, F F, the following mechanism is employed: Each cylinder has an axle, to which is affixed a crank, Q, connected by means of a rod, R, with the slide, G. These axles are also provided with toothed sectors, L L, which gear with two screws, L L, whose threads run in opposite directions. These screws are mounted on a shaft, N, which may be revolved by any suitable arrangement. [Illustration: ROLLING MILL FOR MAKING CORRUGATED IRON] * * * * * RAILWAY TURN-TABLE IN THE TIME OF LOUIS XIV. The small engraving which we reproduce herewith from _La Nature_ is deposited at the Archives at Paris. It is catalogued in the documents relating to Old Marly, 1714, under number 11,339, Vol. 1. The design represents a diversion called the _Jeu de la Roulette_ which was indulged in by the royal family at the sumptuous and magnificent chateau of Mary-le-Roi. [Illustration: PLEASURE CAR; RAILWAY AND TURN-TABLE OF THE TIME OF LOUIS XIV.] According to Alex. Guillaumot the apparatus consisted of a sort of railway on which the car was moved by manual labor. In the car, which was decorated with the royal colors, are seen seated the ladies and children of the king's household, while the king himself stands in the rear and seems to be directing operations. The remarkable peculiarity to which we would direct the attention of the reader is that this document shows that the car ran on rails very nearly like those used on the railways of the present time, and that a turn-table served for changing the direction to a right angle in order to place the car under the shelter of a small building. The picture which we reproduce, and the authenticity of which is certain, proves then that in the time of Louis XIV. our present railway turn-tables had been thought of and constructed--which is a historic fact worthy of being noted. It is well known that the use of railways in mines is of very ancient date, but we do not believe that there are on record any documents as precise as that of the _Jeu de la Roulette_ as to the existence of turn-tables in former ages. * * * * * NEW SIGNAL WIRE COMPENSATOR. _To the Editor of the Scientific American_: