Trevithick' s figures show the working power of the 33-inch pole as much greater than Watt's 72-inch cylinder engine, even when the steam pressure in the former was much reduced, and that Woolf's double-cylinder engine, of less power, cost ten times as much as the pole-engine. This sum probably included the costly buildings required for the beam-engines, which Trevithick's plan dispensed with.
The reader may judge of the perfection of mechanism in this plain-looking engine from the fact that a pole, with 150 lbs. of steam to the inch in the boiler, was equal to 50 or 60 tons weight, thrown up and down its 10-feet stroke ten or fourteen times a minute, with a limit of movement perfectly under control, while modern engineers are building ships' turrets because of the difficulty of raising and depressing a 30-ton gun from the hold to above the water level.
[Rough draft.]
"Camborne, September 12th, 1815.
"Sir,
"I received a letter dated the 20th of August, from Mr. Davies, in which he did not mention the name of Herland castings. On the 24th of the same month I wrote to you, informing you of the same, and requesting to know what state of forwardness the castings were in. On the 30th of August I received another letter from Mr. Davies, not saying what state of forwardness the castings were in, nor when they would be finished, only that they would set their hands about them, and that I might expect a letter from you stating the particulars, which has not yet come to hand. I have waited so long that I am quite out of patience. You will know that it is now nearly double the time that the castings were to have been finished in, and you have not yet answered my letters as to the state of the castings nor when they will be finished. I must again request you to write to me on this subject, otherwise I must immediately remove the orders to some other founders that may be a little more attentive to their customers. I must be informed in the positive, whether the castings will be at Bristol by the next spring-tide, as a vessel is engaged for the purpose of taking them to Cornwall.
"Yours, &c.,
"R. T..
"Mr. John Rastrick,
"Chepstow, South Wales."
Rastrick, whom he had known at the Thames Driftway, had become the managing engineer at the Bridgenorth Foundry.