The volume of air included between the two pistons is displaced at every stroke, so that, according to the position occupied by the pistons, it is held either by the large or small cylinder. The necessary result of this is that a compression of the air, and consequently a resistance, is brought about. In order to obviate this inconvenience, the constructor has connected the space between the two pistons at the part, A', of the frame by a bent pipe. The air, being alternately driven into and sucked out of this chamber, A', of relatively large dimensions, no longer produces but an insignificant resistance. [Illustration: FARCOT'S SIX H.P. STEAM ENGINE. Fig. 1.--Longitudinal Section (Scale 0.10 to 1). Fig. 2.--Horizontal Section (Scale 0.10 to 1). Fig. 3.--Section across the Small Cylinder (Scale 0.10 to 1). Fig. 4.--Section through the Cross Head (Scale 0.10 to 1). Fig. 5.--Application for a Variable Expanion (Scale 0.10 to 1).] As shown in Fig. 5, there may be applied to this engine a variable expansion of the Farcot type. The motor being a single acting one, a single valve-plate suffices. This latter is, during its travel, arrested at one end by a stop and at the other by a cam actuated by the governor. Upon the axis of this cam there is keyed a gear wheel, with an endless screw, which permits of regulating it by hand. This engine, which runs at a pressure of from 5 to 6 kilogrammes, makes 150 revolutions per minute and weighs 2,000 kilogrammes. --_Annales Industrielles_. * * * * * FOOT LATHES. We illustrate a foot lathe constructed by the Britannia Manufacturing Company, of Colchester, and specially designed for use on board ships. These lathes, says _Engineering_, are treble geared, in order that work which cannot usually be done without steam power may be accomplished by foot. For instance, they will turn a 24 inch wheel or plate, or take a half-inch cut off a 3 inch shaft, much heavier work than can ordinarily be done by such tools. They have 6 inch centers, gaps 71/2 inches wide and 61/2 inches deep, beds 4 feet 6 inches long by 83/4 inches on the face and 6 inches in depth, and weigh 14 cwt. There are three speeds on the cone pulley, 9 inches, 6 inches, and 4 inches in diameter and 11/2 inches wide. The gear wheels are 9/16 inch pitch and 11/2 inches wide on face. The steel leading screw is 11/2 inches in diameter by 1/4 inch pitch. Smaller sizes are made for torpedo boats and for places where space is limited. [Illustration: LATHE FOR USE ON SHIPBOARD.] * * * * * ENDLESS TROUGH CONVEYER. [Illustration]