Disqualified by age and ill health from undertaking minute investigations, I find it will be easier for me to state to you my proposition of a lock.-dock, for laying up vessels, high and dry, than to investigate yours. you will then judge for yourself whether any part of mine has anticipated any part of yours.

While I was at Washington, in the administration of the government, Congress was much divided in opinion on the subject of a Navy, a part of them wishing to go extensively into the preparation of a fleet, another part opposed to it, on the objection that the repairs and preservation of a ship, even idle in harbor, in 10. or 12. years amount to her original cost. it has been estimated in England, that if they could be sure of peace a dozen years, it would be cheaper for them to burn their fleet, and build a new one when wanting, than to keep the old one in repair during that term. I learnt that, in Venice there were then ships, lying on their original stocks, ready for launching at any moment, which had been so for 80. years, and were still in a state of perfect preservation; and that this was effected by disposing of them in docks pumped dry, and kept so by constant pumping. it occurred then to me that this expence of constant pumping might be saved by combining a lock with the common wet dock, wherever there was a running stream of water, the bed of which, within a reasonable distance was of a sufficient height above the high water level of the harbor. this was the case at the Navy yard on the Eastern branch at Washington, the high water line of which was 78. feet lower than the ground on which the capital stands, and to which it was found that the water of the Tyber creek could be brought for watering the city. my proposition then was as follows. let ab be the high water level of the harbor, and the vessel to be laid up draw 18 f water. make a chamber A 20 f deep below high water and 20 f high above it. as c.d. e.f. and at the upper end make another chamber B.

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the bottom of which, should be in the high water level, and the top 20. f above that. g.h. is the water of the Tyber when a vessel is to be introduced open the gate at c.b.d. the tide water rises in the chamber A. to the level b.i. and floats the vessel in with it. shut the gate c.b.d. and open that at f.i. the water of the Tyber fills both chambers to the level c.f.g and the vessel floats into the chamber B. then opening both gates c.b.d and f.i. the water flows out, and the vessel settles down on the stays previously prepared at the bottom i.k to recieve her. the gate at g.k. must of course be closed and the water of the feeding stream be diverted elsewhere. The chamber B. is to have a roof over it of the construction of that over the meat market at Paris except that that is hemispherical, this semi cylindrical. for this construction see Duhamel’s architecture whose invention it was. the diameter of the Dome of the meat market is considerably over 100. feet.

It will be seen at once that, instead of making the chamber B. of sufficient width and length for a single vessel only, it may be widened to whatever span the semicircular framing of the roof can be trusted, and to whatever length you please, so as to admit 2. or more vessels in breadth, and as many in length as the localities render expedient.

I had a model of this lock-dock made and exhibited in the President’s house, during the session of Congress at which it was proposed. but the advocates for a navy did not fancy it, and those opposed to the building of ships altogether, were equally indisposed to provide protection for them. ridicule was also resorted to, the ordinary substitute for reason, where that fails & the proposition was past over. I then thought and still think the measure wise, to have a proper number of vessels always ready to be launched, with nothing unfinished about them, except the planting their masts which must of necessity be omitted, to be brought under a roof. having no view in this proposition but to combine for the public a provision for defence, with economy in it’s preservation, I have thought no more of it since and if any of my ideas anticipated yours, you are welcome to appropriate them to yourself, without objection on my part, and, with this assurance, I pray you to accept that of my best wishes and respects.

Th: Jefferson