AMERICAN INSTITUTE. 609 



end of the stroke. But in proportion as the motion is concen- 

 trated, by lengthening the slot, and running the side-block near 

 to the shaft, the commencement of the exhaust is ^delayed, and 

 thus premature release and compression are avoided, and the 

 motion for a half-stroke cut-oft", is so rapid that the exhaust is 

 wide open when the crank pin is an eighth of an inch past the 

 dead point, and remains wide open until almost the end of the 

 stroke. 



Between these two extreme movements, the one so concentrated 

 that it cannot be much varied from half-stroke, and the other 

 simply like the eccentric link motion, we may obtain any degree 

 of concentration required for the service of the engine. If the 

 angular motion of the rockshafts be within 60"^ the link may be 

 forged in the rockshaft, and the radius link be sustained by a han- 

 ger, as in the stationary link motion, as it is inaptly called. But if 

 more concentration is required, and therefore more angular motion 

 is given, the link must be separated from the rockshaft, so that 

 its angular motion may not be inconveniently great ; or a differ- 

 ent means of moving its slide-block must be used. I believe 

 means may be devised to slide the block to any extent, however 

 great the angular motion; and that the two rockshafts, with a 

 reversing gear not much more cumbrous than that now in use, 

 will give any series of motions between these extremes, the varia- 

 bility of expansion being greater as the angular motion is less. 



In a steam carriage it will be expedient to place the pumps near 

 the boiler, remote from the crossheads, to avoid danger of freez- 

 ing, and so keep them within sight and reach of the steersman. 

 In this case rockshafts with slight angular motion, (if sliding joints 

 are used,) will be required to work them, and from the pump 

 rockshafts we can take the motion of the cut-offend of the lever. 

 In this case we may give an extremely quick motion to the main 

 end, making the release and admission rapid, and the cut-off slow, 

 but variable from nothing to full stroke. This motion would cut 

 off quicker than the common link for all admissions less than 

 half stroke, but slower in all admissions greater than half stroke; 

 and the openings to steam would in all admissions be more 

 ample than those of the common link. This is the movement I 

 shall use on steam carriages that are to run on hilly roads, be- 

 cause it gives a delicate means of retarding. When descending 

 a hill it will admit steam in reverse for the last inch or quarter 

 inch of the stroke, or for any extent required to restrain the 

 speed. 



