62 ANNUAL OF SCIENTIFIC DISCOVERY. 



The question has also been recently tested in New York, on a small scale, 

 by running a shaft with one end between wood and the other between brass 

 bearings, both equally loaded by levers like safety valves, and covered with 

 water to insure coolness. During 18 hours the brass wore off about 1-1 6th 

 of an inch, while the wood had not worn to any extent that was appreciable. 

 It is now being tried with a harder kind of brass. 



PERRY'S VALVE MOTION. 



The engines employed in the screw propellers on our Upper Lakes have 

 usually been single high-pressure cylinders, mounted perpendicularly over the 

 crank, but this style is now giving way for the introduction of the more com- 

 pact oscillatory. An extremely simple valve-motion for this style of engine 

 has been lately devised by Mr. H. 0. Perry, and which has become very 

 popular. An oscillating engine is hung on trunnions like a cannon, and its 

 rocking motion as the crank revolves seriously deranges all the usual methods 

 of working the valve. Mr. Perry employs a rotating or partially rotating 

 valve, serving its purpose in a manner precisely similar to the ordinary slide- 

 valve employed on locomotives and small stationary engines. The ports are 

 arranged as usual, but the cylinder-face, on which the valve rests, is curved 

 instead of flat, and the valve is in short a slide bent to fit the cylinder-face. 

 These curved surfaces form a portion of a true cylinder, and the desired 

 sliding motion is obtained by partially revolving a shaft which extends along 

 its axis. It must be understood that this shaft extends across and not length- 

 wise of the main working cylinder, and projects at the side rather than at the 

 end of the steam-chest. On the projecting portion of this shaft is a sweh 1 

 containing a socket in which the starting bar may be inserted for working by 

 hand, and also two arms extending in nearly opposite directions, with a wrist- 

 pin at each extremity. By connecting one of these wrist-pins to any fixed 

 point the rocking of the cylinder gives a motion to the valve which would 

 be exactly the motion desired except for the absence of what is technically 

 termed " lead." To obtain just the proper motion the pin is connected by a 

 suitable rod, not to a fixed point, but to a small excentric on the main shaft, 

 the excentric being keyed in such position as to give the lead, or in other 

 words, make the valve uncover the port and admit steam to the cylinder a 

 little before the commencement of the stroke. In backing the engine this rod 

 is thrown out of use, and the other wrist-pin is connected in a similar manner 

 to another excentric, by which means a perfect reverse motion is obtained. 



The great simplicity of the arrangement will at once be obvious. A steam- 

 chest of little more than rtie ordinary height, with a slight shaft protruding 

 through a stuffing-box in its side, a couple of short arms thereon (that 

 extending upward being somewhat the longer to compensate for the 

 increased motion of that point, due to its greater distance from the line of the 

 trunnions), and two excentrics, with suitable excentric rods and hooks con- 

 nected together, constitute the whole of this ordinarily complex apparatus. 

 The overhanging end of the rocking shaft being of considerable length an 

 additional support is usually provided, consisting of a suitable arm rising 

 from the trunnion. 



