Seth,
I found the floppy; unfortunately, it is corrupted and unrecoverable. I had originally used a set of volumes (books, imagine that!) that had his writings and communications. I no longer have access to them; however, I have found a number of web sites devoted to the same thing. I will have to research Jefferson's writings and get back to you. As I remember, I think it was in a portion of his writings when he was discussing monopolies. Probably after 1788 as prior to this time he was quite adamant in his opposition to any (government sanctioned) monopoly.
Fourth, another hotly debated issue during the drafting stage of both the Copyright Clause of the Constitution and Copyright Act of 1790 was the duration of copyright. Initially duration was to be based on the average life span of authors. Thus under the Copyright Act of 1790, the duration of copyright was set at 14 years with the possibility of renewal for another 14 years if the author was still alive. Thomas Jefferson based a proposed term for copyright on the principle that "the earth belongs in usufruct to the living", and computed it by means of actuarial tables:
Generations, changing daily by daily deaths
and births, have one constant term, beginning at the date of their contract,
and ending when a majority of those of full age at that date shall be dead.
The length of that term may be estimated from tables of mortality [and is
found to be] 18 years 8 months, or say 19 years as the nearest integral number... The principle, that the earth belongs to the living, and
not to the dead, is of very extensive application... Turn this subject in
your mind, my dear Sir... and develop it with that perspicuity and cogent
logic so peculiarly yours... Establish the principle...
in the new law to be passed for protecting copyrights and new inventions,
by securing the exclusive right for 19 instead of 14 years. (Jefferson,
Letter to James Madison, September 6, 1789)
also:It may be said that the succeeding generation exercising in fact the power of repeal, this leaves them as free as if the constitution or law had been expressly limited to 19. years only. In the first place, this objection admits the right, in proposing an equivalent. But the power of repeal is not an equivalent. It might be indeed if every form of government were so perfectly contrived that the will of the majority could always be obtained fairly and without impediment. But this is true of no form. The people cannot assemble themselves; their representation is unequal and vicious. Various checks are opposed to every legislative proposition. Factions get possession of the public councils. Bribery corrupts them. Personal interests lead them astray from the general interests of their constituents; and other impediments arise so as to prove to every practical man that a law of limited duration is much more manageable than one which needs a repeal.
"The saying there shall be no monopolies lessens the incitements to ingenuity, which is spurred on by the hope of a monopoly for a limited time, as of fourteen years; but the benefit of even limited monopolies is too doubtful to be opposed to that of their general suppression." --Thomas Jefferson to James Madison, 1788. ME 7:98
from http://etext.lib.virginia.edu/jefferson/quotations/jeff1320.htm