A simple and compact form of slide sleeve valve gear has been developed in England that is of more than passing interest. It permits of a maximum area for both the inlet and exhaust gases which of course keeps the velocity and back pressure at a minimum for a given valve lift. The small lift also insures noiseless operation and a small amount of wear. The sleeve is balanced at the end of the working stroke. The combustion chamber is nearly hemispherical in shape which reduces the heat loss to the walls. [Illustration: Fig. 34. Reeves Slide Valve Gear. ] Referring to the section of the end of cylinder given in the diagram, (34) A is an open-ended water-jacketed cylinder in which the piston B works. At the upper end of the cylinder is attached a ring C forming an extension of the stationary cylindrical head D carrying the sparking plug. At the lower end of the head D is provided a seating E for the sliding cylindrical inlet valve F, which takes its bearing around the circular head. This inlet valve is provided with expanding rings G to keep it gas-tight. Surrounding the inlet valve F is a second cylindrical exhaust valve H, which is provided with an angular seating at J. The outer circumference of the cylindrical exhaust valve H bears against the walls of the cylinder. Cast in the cylinder is an annular space K communicating with a passage L for the admission of the inlet gases. These pass through suitable ports cut in the sides of the exhaust valve H and the inlet valve F, so that they are free to pass through the space made when the inlet valve F is lowered from its seat. A similar type of annular space M is cast in the cylinder in connection with an opening O for the passage of the exhaust gas when the cylindrical valve H is raised from its seating at J. The cylinder head is not water jacketed as the builder states that the continual passage of the intake gases keeps it reasonably cool. The exhaust passages are thoroughly water cooled. (51) Argyll Single Sleeve Motor. The Argyll sliding sleeve automobile motor is unique in the fact that only one sleeve is used to control both the inlet and exhaust gases instead of the two sleeves commonly used on the Knight motor. This sleeve, instead of having either a purely vertical or horizontal motion, has a peculiar combination of the two, that is to say, it moves a certain amount in rotation within the cylinder, and an equal amount vertically, the combined motion constituting an ellipse. The external appearance of the engine is shown by Fig. 35, which will give an idea of the general arrangement of the cylinders, ports and piping.