PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 633 



t 

 connected with each other bj' two steam channels e and /, one of which e 



is for direct sleani and the other / for the exhaust, although in reversing 

 the engine e becomes the exhaust and f the steam passage. The pistons 

 are cylindrical and take up sufficient space to lap over the openings of the 

 steam channels c and f where those enter the cylinders and are shaped as 

 shown at g. In the sides of the piston cliannels or recesses are cut, on 

 opposite sides proper to meet the steam passages, when the piston is 

 moved along the cylinder, so that they shall stand over their openings. It 

 is to be understood that the valve does not operate the steam for its own 

 cylinder, but always for the cylinder next preceding it. Thus the valve 

 in the cylinder a regulates the flow of steam to and from the cylinder b, 

 and b for c, c for d, and d for a. There are six steam openings into each 

 cylinder, viz: e and f leading from b to c, and e' and /' leading from a to 

 b on the opposite side, and so likewise for the other two cylinders, and 

 lying in the same plane. The other two openings enter on opposite sides 

 of the cylinder at a right angle to -those first named and as shown by the 

 dotted lines h /i' and i i' in cylinders a and b. The openings h and h\ as 

 also the similar openings in the other cylinder, all lead to one common 

 receiving pipe for the admission of steam, as shown at k, figs. 1 and 2, 

 ^•' being the branch pipe for connecting all the cylinders with it. The 

 openings t i' also lead in like manner to one common exit pipe I through 

 Z' in like manner. The valve j, fig. 2, is shown as closing both pipes, and 

 the engine is accordingly at rest. The valve on each piston acts precisely 

 as the D slide valve of ordinary engines. At n m are recesses on one side 

 of the valve g. One of these n passes round one quarter of the circumfer- 

 ence of the cylinder on the under side, while m extends in like manner one 

 quarter on the opposite or upper side. It will be thus seen that when the 

 piston g has moved along so that the channel n stands opposite e it will 

 also be over tlie opening h, so that steam will pass at once into the cylinder 

 e. The same is also true of m, for when that recess is opposite f it will 

 also stand over the opening i, and the steam can flow out of the cylinder o 

 as shown. On the opposite side of the jiiston g there is another opening 

 for receiving and discharging the steam according to the working of the 

 valve in a. This opening is seen at o and extends through the narrow 

 channel o' up and through the piston, thus communicating with the steam 

 space between the piston and the head of the cylinder; as shown, it over- 

 laps the two ports e' and/', and acts in that respect like an ordinary slide 

 valve. The crank is placed in the opening in the frame at the inner ends 

 of the four cylinders as seen at p, that being the crank pin. Four con- 

 necting r(jds, each attached to one of the four pistons, are joined to the 

 crank pin. As the cylinders stand at right angles to each other there is 

 necessarily always one or two pistons in action upon the crank, so that 

 when any pair of pistons which stand opposite to each other are at the end 

 of their strokes the other two will be at the half of their stroke. Thus 

 the piston in a is at half stroke, moving toward the crank, c is also at half 

 stroke retreating from the crank, and b and d at the extremity of their 

 respective strokes. Now, it is when the pistons are at half stroke that 

 the valves begin to operate upon the steam for the preceding cylinder, 

 either to admit or exhaust the steam as may be required. It will be seen 



