608 TRANSACTIONS OF THE 



tions against it are well founded, and that if a valve could be 

 moved suddenly, and yet smoothly, and by an apparatus as sim- 

 ple as the link, it would be a great improvement. And in this 

 opinion I am sustained by many of the American locomotive 

 builders of this time, who still reject the link on account of its 

 wiredrawing and compression, and resort to separate cut-oft' valves, 

 to cause movements, and other means to obtain quick and full 

 openings, even at the sacrifice of simplicity, and sometimes of 

 smooth action, I confess that I may be biased in this opinion. I 

 have invented a link valve motion, which is concentrated in its 

 action, and yet smooth. Many of the members of this Club have 

 seen ray plan exhibited in a rude model, and constructed on my 

 experimental steam carriage, for variable expansion; but I have 

 a simpler form of it, for half-stroke, which will soon be applied 

 in a case in which a half-stroke movement is preferable to any 

 other. As the rules of the Ckib encourage me to make known 

 my plan, by its means, I will avail myself of this occasion to de- 

 scribe it, and to compare its action with that of the link, as con- 

 structed by Rogers; and I expect to show that the expansion can 

 be carried as far with this half-stroke movement, as it can be 

 carried with the. link on the Rogers engine; and that it can do 

 heavy work better than a movement that cuts oft" later than half- 

 stroke, provided the pressure of steam is sufficient. 



The apparatus consists of two rockshafts, which receive mo- 

 tion from the crossheads. They are placed one over 'the other. 

 Each shaft has an arm which gives the lead and cut-off' to the 

 valve of its own engine, and another arm which gives the main 

 movement to the valve of the other engine. Converting links 

 from these arms are joined to the ends of a lever, the middle of 

 which is jointed to the valve stem. If the motion given to the 

 rock shafts be slow, like the eccentric motion, the effect will be 

 to give tlie same series of motions that are given by the common 

 link; but if the arms by which they receive motion from the 

 crosshead be slotted, and fitted with slide blocks, so that at the 

 middle of their movement they have a short leverage, the move- 

 ment will be concentrated — it will be slow at both ends, and 

 rapid in the middle, and the valve stem lever will divide it into 

 two steps; the first carrying the lip of the valve over the port, 

 cutting off", and giving the linear advance usually given by the 

 angular advance of the eccentrics, equal to the lap and lead; the 

 other step, derived from the shaft moved by the opposite engine, 

 giving the train movement; and the exhaust, of course, has what- 

 ever lead may be deemed best — I put it seven-eighths open at the 



