POLE STEAM-ENGINE. 79 



only space enough between the pole and the cylinder to prevent 

 friction, or, in case the steam is admitted near the stuffing box, 

 I leave sufficient room for the steam to pass to the bottom of 

 the cylinder, and I do make at the upper end of the cylinder for 

 the plunger-pole to pass through a stuffing box of much greater 

 depth than usual, into which stuffing box I do introduce enough 

 of the usual packing to fill it one-third high. Upon this packing 

 I place a ring of metal, occupying about another third part of 

 the depth of the stuffing box, this ring having a circular groove 

 at the inside, and a hole or holes through it communicating 

 with the outside, and with a hole through the side of the stuffing 

 box ; or, instead of one ring containing a groove, I sometimes 

 place two thinner rings, kept asunder by a number of pillars to 

 about the distance of one-third of the depth of the stuffing box, 

 and I pack the remaining space above the ring or rings, and 

 secure the whole down in the usual manner. The intention of 

 this arrangement is to produce the effect of two stuffing boxes, 

 allowing a space between the two stuffings for water to pass 

 freely in from the boiler or forcing pump through a pipe and 

 through the hole in the side of the stuffing box, so as to 

 surround the plunger-pole and form the ring of water for the 

 purpose of preventing the escape of steam by keeping up an 

 equilibrium between the water above the lower stuffing and the 

 steam in the cylinder. By this part of my said invention I 

 obviate the necessity of that tight packing which is requisite 

 when steam of a high pressure is used, and consequently I avoid 

 a greater proportion of the usual friction, because a very 

 moderate degree of tightness in the packing is quite sufficient 

 to prevent the passage of any injurious quantity of so dense a 

 fluid as water. And I do further declare that I use the plunger- 

 pole, working in a cylinder and through a double stuffing, either 

 with or without a condenser, according to the nature of the work 

 which the steam-engine is to perform." 



Though Trevithick has been spoken of as a visionary, 

 intractable schemer, observation shows that he adhered 

 with tenacity to original ideas, proved to be good. 

 The plunger-pole pump, the water-pressure engine, the 



