CATALOG OF THE MECHANICAL COLLECTIONS 79 



slide in the same direction. As a result, the governor slide is <?iven 

 a greater motion for a given change in speed than would otherwise 

 result. 



DROP CUT-OFF VALVE AND MECHANISM 



U.S.N.M, no. 309819 ; model ; gift of the Franklin Machine Co. ; not illustrated. 

 This is a wooden model of a very simple variable drop cut-off 

 valve gear in which a poppet valve is lifted by a bell crank operated 

 by a cam. The cam is a cylinder that may be moved parallel to its 

 axis, so as to bring any part of the cam against the follower of the 

 bell crank. The cam is so shaped that the valve will open at the 

 same time for all positions of the cam, but the valve will close 

 progressively earlier or later as the cam is moved along its shaft. 



GOVERNOR AND THROTTLE VALVE 



U.S.N.M. no. 309818; model; gift of the Franklin Machine Co.; not illustrated. 



This is a crank-operated, wooden model of a ball governor con- 

 nected to a throttle valve in a short section of pipe. 



The governor consists of balls hung in the usual manner upon arms 

 attached by pin joints at their upper ends to the top of the governor 

 spindle. Radius rods from the centers of the ball arms connect to a 

 collar upon the spindle, so that the collar moves up and down as the 

 balls are swung in or out by changes in the speed of the engine. The 

 sliding collar is connected to a crank on the axis of the disk of a plain 

 butterfly valve. 



CORLISS MARINE-BOILER IMPROVEMENTS, 18G2 



U.S.N.M. no. 308666; original patent model; transferred from the United States 

 Patent Office; not illustrated. 



This model was submitted with the application for the patents 

 issued to George H. Corliss, Providence, R. I., August 26, 1862, nos. 

 36279 and 36281. 



The model represents a pair of internally fired, fire-tube boilers of 

 the "locomotive" type, each equipped with a steam main connected to 

 the steam space at six different points for the purpose of diffusing the 

 draft of steam from over the whole surface of the water in the boiler 

 and thus prevent priming ; and provided with a salt-water evaporator 

 located in the breeching, so as to obtain heat from the hot flue gases, 

 and connected to the surface condenser to lower the pressure on the 

 boiling salt water to facilitate evaporation. 



The purpose of the peculiar arrangement of steam pipes is to pro- 

 vide a method of obtaining steam free from water without the neces- 

 sity of a high steam chamber, which would be a vulnerable part of a 

 naval vessel. The theory is that the filling of any of the many tubes 



