"The duty, I doubt not, will be, both for water and air sides condensing, at least 50 per cent. above our Cornish engines, which will be above four times what is now done with ships' engines, especially when you take into consideration their getting steam from salt water, and letting out so much water from the boiler to prevent the salt from accumulating in the boiler, which will make 30 per cent. more in its favour.
"If strong boilers to stand 200 lbs. to the inch are made with small tubes, I have no doubt but that the duty would be considerably more, and my engines will not be one-quarter part of the weight, price, or space of others; and when every advantage is taken it will be 1000 per cent. superior in saving of coal to those now at work on board. This engine works well, and returns the steam very regularly every stroke into the boiler.
"I am extremely sorry you were not present to see these experiments. Please make your remarks on these statements, with any further information you may judge useful.
"I shall now make drawings agreeable to my experiments for actual performance on board ships. In hope of hearing from you soon,
"I remain, Sir,
"Your very humble servant,
"Richard. Trevithick.
The large old boilers used as surface condensers, in which the steam was partially condensed by the transmission of heat to the external atmosphere, together with its further condensation in a smaller condenser with cold water around it, so reduced its expansiveness, that a large feed-pump drew the hot water and steam from the small condenser, and forced it back into the boiler without any reduction of quantity; those temporary contrivances, almost immediately resolved themselves into a condenser made of copper tubes surrounded by cold water.
Having proved by six months' experiment on a working scale the practicability of the plan which in reality he had invented twenty years before in the iron steamship,[173] he wrote in June, 1830:—
"To the Right Honourable the Lords Commissioners of the Admiralty, &c., &c., &c.
"My Lords,