_To Isaac McPherson_
        _Monticello, August 13, 1813_

        SIR, -- Your letter of August 3d asking information on the
subject of Mr. Oliver Evans' exclusive right to the use of what he
calls his Elevators, Conveyers, and Hopper-boys, has been duly
received.  My wish to see new inventions encouraged, and old ones
brought again into useful notice, has made me regret the
circumstances which have followed the expiration of his first patent.
I did not expect the retrospection which has been given to the
reviving law.  For although the second proviso seemed not so clear as
it ought to have been, yet it appeared susceptible of a just
construction; and the retrospective one being contrary to natural
right, it was understood to be a rule of law that where the words of
a statute admit of two constructions, the one just and the other
unjust, the former is to be given them.  The first proviso takes care
of those who had lawfully used Evans' improvements under the first
patent; the second was meant for those who had lawfully erected and
used them after that patent expired, declaring they "should not be
liable to damages therefor." These words may indeed be restrained to
uses already past, but as there is parity of reason for those to
come, there should be parity of law.  Every man should be protected
in his lawful acts, and be certain that no _ex post facto_ law shall
punish or endamage him for them.  But he is endamaged, if forbidden
to use a machine lawfully erected, at considerable expense, unless he
will pay a new and unexpected price for it.  The proviso says that he
who erected and used lawfully should not be liable to pay damages.
But if the proviso had been omitted, would not the law, construed by
natural equity, have said the same thing.  In truth both provisos are
useless.  And shall useless provisos, inserted _pro majori cautela_
only, authorize inferences against justice?  The sentiment that _ex
post facto_ laws are against natural right, is so strong in the
United States, that few, if any, of the State constitutions have
failed to proscribe them.  The federal constitution indeed interdicts
them in criminal cases only; but they are equally unjust in civil as
in criminal cases, and the omission of a caution which would have
been right, does not justify the doing what is wrong.  Nor ought it
to be presumed that the legislature meant to use a phrase in an
unjustifiable sense, if by rules of construction it can be ever
strained to what is just.  The law books abound with similar
instances of the care the judges take of the public integrity.  Laws,
moreover, abridging the natural right of the citizen, should be
restrained by rigorous constructions within their narrowest limits.

        Your letter, however, points to a much broader question,
whether what have received from Mr. Evans the new and proper name of
Elevators, are of his invention.  Because, if they are not, his
patent gives him no right to obstruct others in the use of what they
possessed before.  I assume it is a Lemma, that it is the invention
of the machine itself, which is to give a patent right, and not the
application of it to any particular purpose, of which it is
susceptible.  If one person invents a knife convenient for pointing
our pens, another cannot have a patent right for the same knife to
point our pencils.  A compass was invented for navigating the sea;
another could not have a patent right for using it to survey land.  A
machine for threshing _wheat_ has been invented in Scotland; a second
person cannot get a patent right for the same machine to thresh
_oats_, a third _rye_, a fourth _peas_, a fifth _clover_, &c.  A
string of buckets is invented and used for raising water, ore, &c.,
can a second have a patent right to the same machine for raising
wheat, a third oats, a fourth rye, a fifth peas, &c?  The question
then whether such a string of buckets was invented first by Oliver
Evans, is a mere question of fact in mathematical history.  Now,
turning to such books only as I happen to possess, I find abundant
proof that this simple machinery has been in use from time
immemorial.  Doctor Shaw, who visited Egypt and the Barbary coast in
the years 1727-8-9, in the margin of his map of Egypt, gives us the
figure of what he calls a Persian wheel, which is a string of round
cups or buckets hanging on a pully, over which they revolved,
bringing up water from a well and delivering it into a trough above.
He found this used at Cairo, in a well 264 feet deep, which the
inhabitants believe to have been the work of the patriarch Joseph.
Shaw's travels, 341, Oxford edition of 1738 in folio, and the
Universal History, I. 416, speaking of the manner of watering the
higher lands of Egypt, says, "formerly they made use of Archimedes's
screw, thence named the Egyptian pump, but they now generally use
wheels (wallowers) which carry a rope or chain of earthen pots
holding about seven or eight quarts apiece, and draw the water from
the canals.  There are besides a vast number of wells in Egypt, from
which the water is drawn in the same manner to water the gardens and
fruit trees; so that it is no exaggeration to say, that there are in
Egypt above 200,000 oxen daily employed in this labor." Shaw's name
of Persian wheel has been since given more particularly to a wheel
with buckets, either fixed or suspended on pins, at its periphery.
Mortimer's husbandry, I. 18, Duhamel III. II., Ferguson's Mechanic's
plate, XIII; but his figure, and the verbal description of the
Universal History, prove that the string of buckets is meant under
that name.  His figure differs from Evans' construction in the
circumstances of the buckets being round, and strung through their
bottom on a chain.  But it is the principle, to wit, a string of
buckets, which constitutes the invention, not the form of the
buckets, round, square, or hexagon; nor the manner of attaching them,
nor the material of the connecting band, whether chain, rope, or
leather.  Vitruvius, L. x. c. 9, describes this machinery as a
windlass, on which is a chain descending to the water, with vessels
of copper attached to it; the windlass being turned, the chain moving
on it will raise the vessel, which in passing over the windlass will
empty the water they have brought up into a reservoir.  And Perrault,
in his edition of Vitruvius, Paris, 1684, fol. plates 61, 62, gives
us three forms of these water elevators, in one of which the buckets
are square, as Mr. Evans' are.  Bossut, Histoire de Mathematiques, i.
86, says, "the drum wheel, the wheel with buckets and the
_Chapelets_, are hydraulic machines which come to us from the
ancients.  But we are ignorant of the time when they began to be put
into use." The _Chapelets_ are the revolving bands of the buckets
which Shaw calls the Persian wheel, the moderns a chain-pump, and Mr.
Evans elevators.  The next of my books in which I find these
elevators is Wolf's Cours de Mathematiques, i. 370, and plate 1,
Paris 1747, 8vo; here are two forms.  In one of them the buckets are
square, attached to two chains, passing over a cylinder or wallower
at top, and under another at bottom, by which they are made to
revolve.  It is a nearly exact representation of Evans' Elevators.
But a more exact one is to be seen in Desagulier's Experimental
Philosophy, ii. plate 34; in the Encyclopedie de Diderot et
D'Alembert, 8vo edition of Lansanne, 1st volume of plates in the four
subscribed Hydraulique.  Norie, is one where round eastern pots are
tied by their collars between two endless ropes suspended on a
revolving lantern or wallower.  This is said to have been used for
raising ore out of a mine.  In a book which I do not possess,
L'Architecture Hidraulique de Belidor, the 2d volume of which is said
[De la Lande's continuation of Montuclas' Historie de Mathematiques,
iii. 711] to contain a detail of all the pumps, ancient and modern,
hydraulic machines, fountains, wells, &c, I have no doubt this
Persian wheel, chain pump, chapelets, elevators, by whichever name
you choose to call it, will be found in various forms.  The last book
I have to quote for it is Prony's Architecture Hydraulique i.,
Avertissement vii., and 648, 649, 650.  In the latter of which
passages he observes that the first idea which occurs for raising
water is to lift it in a bucket by hand.  When the water lies too
deep to be reached by hand, the bucket is suspended by a chain and
let down over a pulley or windlass.  If it be desired to raise a
continued stream of water, the simplest means which offers itself to
the mind is to attach to an endless chain or cord a number of pots or
buckets, so disposed that, the chain being suspended on a lanthorn or
wallower above, and plunged in water below, the buckets may descend
and ascend alternately, filling themselves at bottom and emptying at
a certain height above, so as to give a constant stream.  Some years

before the date of Mr. Evans' patent, a Mr. Martin of Caroline county
in this State, constructed a drill-plough, in which he used the band
of buckets for elevating the grain from the box into the funnel,
which let them down into the furrow.  He had bands with different
sets of buckets adapted to the size of peas, of turnip seed, &c.  I
have used this machine for sowing Benni seed also, and propose to
have a band of buckets for drilling Indian Corn, and another for
wheat.  Is it possible that in doing this I shall infringe Mr. Evans'
patent?  That I can be debarred of any use to which I might have
applied my drill, when I bought it, by a patent issued after I bought

        These verbal descriptions, applying so exactly to Mr. Evans'
elevators, and the drawings exhibited to the eye, flash conviction
both on reason and the senses that there is nothing new in these
elevators but their being strung together on a strap of leather.  If
this strap of leather be an invention, entitling the inventor to a
patent right, it can only extend to the strap, and the use of the
string of buckets must remain free to be connected by chains, ropes,
a strap of hempen girthing, or any other substance except leather.
But, indeed, Mr. Martin had before used the strap of leather.

        The screw of Archimedes is as ancient, at least, as the age of
that mathematician, who died more than 2,000 years ago.  Diodorus
Siculus speaks of it, L. i., p. 21, and L. v., p. 217, of Stevens'
edition of 1559, folio; and Vitruvius, xii.  The cutting of its
spiral worm into sections for conveying flour or grain, seems to have
been an invention of Mr. Evans, and to be a fair subject of a patent
right.  But it cannot take away from others the use of Archimedes'
screw with its perpetual spiral, for any purposes of which it is

        The hopper-boy is an useful machine, and so far as I know,

        It has been pretended by some, (and in England especially,)
that inventors have a natural and exclusive right to their
inventions, and not merely for their own lives, but inheritable to
their heirs.  But while it is a moot question whether the origin of
any kind of property is derived from nature at all, it would be
singular to admit a natural and even an hereditary right to
inventors.  It is agreed by those who have seriously considered the
subject, that no individual has, of natural right, a separate
property in an acre of land, for instance.  By an universal law,
indeed, whatever, whether fixed or movable, belongs to all men
equally and in common, is the property for the moment of him who
occupies it; but when he relinquishes the occupation, the property
goes with it.  Stable ownership is the gift of social law, and is
given late in the progress of society.  It would be curious then, if
an idea, the fugitive fermentation of an individual brain, could, of
natural right, be claimed in exclusive and stable property.  If
nature has made any one thing less susceptible than all others of
exclusive property, it is the action of the thinking power called an
idea, which an individual may exclusively possess as long as he keeps
it to himself; but the moment it is divulged, it forces itself into
the possession of every one, and the receiver cannot dispossess
himself of it.  Its peculiar character, too, is that no one possesses
the less, because every other possesses the whole of it.  He who
receives an idea from me, receives instruction himself without
lessening mine; as he who lights his taper at mine, receives light
without darkening me.  That ideas should freely spread from one to
another over the globe, for the moral and mutual instruction of man,
and improvement of his condition, seems to have been peculiarly and
benevolently designed by nature, when she made them, like fire,
expansible over all space, without lessening their density in any
point, and like the air in which we breathe, move, and have our
physical being, incapable of confinement or exclusive appropriation.

Inventions then cannot, in nature, be a subject of property.  Society
may give an exclusive right to the profits arising from them, as an
encouragement to men to pursue ideas which may produce utility, but
this may or may not be done, according to the will and convenience of
the society, without claim or complaint from any body.  Accordingly,
it is a fact, as far as I am informed, that England was, until
wecopied her, the only country on earth which ever, by a general law,
gave a legal right to the exclusive use of an idea.  In some other
countries it is sometimes done, in a great case, and by a special and
personal act, but, generally speaking, other nations have thought
that these monopolies produce more embarrassment than advantage to
society; and it may be observed that the nations which refuse
monopolies of invention, are as fruitful as England in new and useful

        Considering the exclusive right to invention as given not of
natural right, but for the benefit of society, I know well the
difficulty of drawing a line between the things which are worth to
the public the embarrassment of an exclusive patent, and those which
are not.  As a member of the patent board for several years, while
the law authorized a board to grant or refuse patents, I saw with
what slow progress a system of general rules could be matured.  Some,
however, were established by that board.  One of these was, that a
machine of which we were possessed, might be applied by every man to
any use of which it is susceptible, and that this right ought not to
be taken from him and given to a monopolist, because the first
perhaps had occasion so to apply it.  Thus a screw for crushing
plaster might be employed for crushing corn-cobs.  And a chain-pump
for raising water might be used for raising wheat: this being merely
a change of application.  Another rule was that a change of material
should not give title to a patent.  As the making a ploughshare of
cast rather than of wrought iron; a comb of iron instead of horn or
of ivory, or the connecting buckets by a band of leather rather than
of hemp or iron.  A third was that a mere change of form should give
no right to a patent, as a high-quartered shoe instead of a low one;
a round hat instead of a three-square; or a square bucket instead of
a round one.  But for this rule, all the changes of fashion in dress
would have been under the tax of patentees.  These were among the
rules which the uniform decisions of the board had already
established, and under each of them Mr. Evans' patent would have been
refused.  First, because it was a mere change of application of the
chain-pump, from raising water to raise wheat.  Secondly, because the
using a leathern instead of a hempen band, was a mere change of
material; and thirdly, square buckets instead of round, are only a
change of form, and the ancient forms, too, appear to have been
indifferently square or round.  But there were still abundance of
cases which could not be brought under rule, until they should have
presented themselves under all their aspects; and these
investigations occupying more time of the members of the board than
they could spare from higher duties, the whole was turned over to the
judiciary, to be matured into a system, under which every one might
know when his actions were safe and lawful.  Instead of refusing a
patent in the first instance, as the board was authorized to do, the
patent now issues of course, subject to be declared void on such
principles as should be established by the courts of law.  This
business, however, is but little analogous to their course of
reading, since we might in vain turn over all the lubberly volumes of
the law to find a single ray which would lighten the path of the
mechanic or the mathematician.  It is more within the information of
a board of academical professors, and a previous refusal of patent
would better guard our citizens against harrassment by law-suits.
But England had given it to her judges, and the usual predominancy of
her examples carried it to ours.

        It happened that I had myself a mill built in the interval
between Mr. Evans' first and second patents.  I was living in
Washington, and left the construction to the mill-wright.  I did not
even know he had erected elevators, conveyers and hopper-boys, until
I learnt it by an application from Mr. Evans' agent for the patent
price.  Although I had no idea he had a right to it by law, (for no
judicial decision had then been given,) yet I did not hesitate to
remit to Mr. Evans the old and moderate patent price, which was what
he then asked, from a wish to encourage even the useful revival of
ancient inventions.  But I then expressed my opinion of the law in a
letter, either to Mr. Evans or to his agent.

        I have thus, Sir, at your request, given you the facts and
ideas which occur to me on this subject.  I have done it without
reserve, although I have not the pleasure of knowing you personally.
In thus frankly committing myself to you, I trust you will feel it as
a point of honor and candor, to make no use of my letter which might
bring disquietude on myself.  And particularly, I should be unwilling
to be brought into any difference with Mr. Evans, whom, however, I
believe too reasonable to take offence at an honest difference of
opinion.  I esteem him much, and sincerely wish him wealth and honor.
I deem him a valuable citizen, of uncommon ingenuity and usefulness.
And had I not esteemed still more the establishment of sound
principles, I should now have been silent.  If any of the matter I
have offered can promote that object, I have no objection to its
being so used; if it offers nothing new, it will of course not be
used at all.  I have gone with some minuteness into the mathematical
history of the elevator, because it belongs to a branch of science in
which, as I have before observed, it is not incumbent on lawyers to
be learned; and it is possible, therefore, that some of the proofs I
have quoted may have escaped on their former arguments.  On the law
of the subject I should not have touched, because more familiar to
those who have already discussed it; but I wished to state my own
view of it merely in justification of myself, my name and approbation
being subscribed to the act.  With these explanations, accept the
assurance of my respect.

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