POLE STEAM-ENGTNE. !>3 



worked well with steam of 120 Ibs. to the inch; but 

 the want of strength in the pump-rods and the require- 

 ments of the mine caused the regular working pressure 

 of steam to be reduced to 60 Ibs. on the inch, and to 

 be cut off when the pole had moved through the first 

 quarter of its stroke. The excellent draught causing the 

 fire-bars to be reduced to one-quarter of their original 

 surface, and the heating the feed-water by the waste 

 steam in this powerful pumping engine, indicate the use 

 of the blast-pipe as at that time worked in the Welsh 

 puddling-mill engine. Watt's engine was for a moment 

 forgotten, that he might challenge Woolf to a trial, 

 giving him as a help twenty millions, or the understood 

 duty of the Watt engine. This non-condensing pole- 

 engine, with 20 tons of pump-rods, moved at a maxi- 

 mum speed of 8 feet a second, and was equal to its work 

 with a steam pressure of 52 Ibs. on the 'inch. Trevi- 

 thick contemplated extending the expansive principle 

 even further than he had done in the Wheal Prosper 

 pole condensing engine, so that at the finish of the up- 

 stroke the steam should only be about the pressure of 

 the atmosphere, or say from 1 to 10 Ibs. on the inch, 

 having commenced it with steam of from 100 to 200 Ibs. 

 on the inch, and cutting off the supply from the boiler 

 when the pole had gone but a very small part of its 

 upward stroke, more or less as the mine requirements 

 admitted of it. The principle of expansive working and 

 momentum of moving parts was of necessity modified 

 in its application to pump-work. 



" DEAR TREVITHICK, " EASTBOURNE, February 15th, 1816. 



" I have been called here by the decease of my wife's 

 uncle, and consequently your letters of the llth did not reach 

 me till this day. 



" The account you give me of your new engine has been 



