Though her doom was close upon her and the enemy of prophecy should come that very night through the open, southward door that was named the Gate of the Doom, yet that rocky edifice Thlūnrāna remained mysterious still, venerable, terrible, dark, and dreadfully crowned with her doom. It was not often that anyone dared wander near to Thlūnrāna by night when the moan of the magicians invoking we know not Whom rose faintly from inner chambers, scaring the drifting bats: but on the last night of all the man from the black-thatched cottage by the five pine-trees came, because he would see Thlūnrāna once again before the enemy that was divine, but that dwelt with men, should come against it and it should be no more. Up the dark valley he went like a bold man, but his fears were thick upon him; his bravery bore their weight but stooped a little beneath them. He went in at the southward gate that is named the Gate of the Doom. He came into a dark hall, and up a marble stairway passed to see the last of Thlūnrāna. At the top a curtain of black velvet hung and he passed into a chamber heavily hung with curtains, with a gloom in it that was blacker than anything they could account for. In a sombre chamber beyond, seen through a vacant archway, magicians with lighted tapers plied their wizardry and whispered incantations. All the rats in the place were passing away, going whimpering down the stairway. The man from the black-thatched cottage passed through that second chamber: the magicians did not look at him and did not cease to whisper. He passed from them through heavy curtains still of black velvet and came into a chamber of black marble where nothing stirred. Only one taper burned in the third chamber; there were no windows. On the smooth floor and under the smooth wall a silk pavilion stood with its curtains drawn close together: this was the holy of holies of that ominous place, its inner mystery. One on each side of it dark figures crouched, either of men or women or cloaked stone, or of beasts trained to be silent. When the awful stillness of the mystery was more than he could bear the man from the black-thatched cottage by the five pine-trees went up to the silk pavilion, and with a bold and nervous clutch of the hand drew one of the curtains aside, and saw the inner mystery, and laughed. And the prophecy was fulfilled, and Thlūnrāna was never more a terror to the valley, but the magicians passed away from their terrific halls and fled through the open fields wailing and beating their breasts, for laughter was the enemy that was doomed to come against Thlūnrāna through her southward gate (that was named the Gate of the Doom), and it is of the gods but dwells with man.

Pieces of paper and tall clouds of dust went with him as far as the city's outer gate. He turned then and called to Spring: "You can do nothing in this city," he said; then he marched homeward over plains and sea and heard his old winds howling as he marched. The ice broke up behind him and foundered like navies. To left and to right of him flew the flocks of the sea-birds, and far before him the geese's triumphant cry went like a clarion. Greater and greater grew his stature as he went northwards and ever more kingly his mien. Now he took baronies at a stride and now counties and came again to the snow-white frozen lands where the wolves came out to meet him and, draping himself anew with old grey clouds, strode through the gates of his invincible home, two old ice barriers swinging on pillars of ice that had never known the sun.

So the town was left to Spring. And she peered about to see what she could do with it. Presently she saw a dejected dog coming prowling down the road, so she sang to him and he gambolled. I saw him next day strutting by with something of an air. Where there were trees she went to them and whispered, and they sang the arboreal song that only trees can hear, and the green buds came peeping out as stars while yet it is twilight, secretly one by one. She went to gardens and awaked from dreaming the warm maternal earth. In little patches bare and desolate she called up like a flame the golden crocus, or its purple brother like an emperor's ghost. She gladdened the graceless backs of untidy houses, here with a weed, there with a little grass. She said to the air, "Be joyous."

Children began to know that daisies blew in unfrequented corners. Buttonholes began to appear in the coats of the young men. The work of Spring was accomplished.

One night the Devil appeared unto him in a dream and said "Well done."

"Avaunt," said that earnest man.

"No, no, friend," said the Devil.

"Dare not to call me 'friend,'" he answered bravely.

"Come, come, friend," said the Devil. "Have you not put apart the couples that would dance? Have you not checked their laughter and their accursed mirth? Have you not worn my livery of black? O friend, friend, you do not know what a detestable thing it is to sit in hell and hear people being happy, and singing in theatres and singing in the fields, and whispering after dances under the moon," and he fell to cursing fearfully.

"It is you," said the Puritan, "that put into their hearts the evil desire to dance; and black is God's own livery, not yours."

And the Devil laughed contemptuously and spoke.

"He only made the silly colors," he said, "and useless dawns on hill-slopes facing South, and butterflies flapping along them as soon as the sun rose high, and foolish maidens coming out to dance, and the warm mad West wind, and worst of all that pernicious influence Love."

And when the Devil said that God made Love that earnest man sat up in bed and shouted "Blasphemy! Blasphemy!"

"It's true," said the Devil. "It isn't I that send the village fools muttering and whispering two by two in the woods when the harvest moon is high, it's as much as I can bear even to see them dancing."

"Then," said the man, "I have mistaken right for wrong; but as soon as I wake I will fight you yet."

"O, no you don't," said the Devil. "You don't wake up out of this sleep."

And somewhere far away Hell's black steel doors were opened, and arm in arm those two were drawn within, and the doors shut behind them and still they went arm in arm, trudging further and further into the deeps of Hell, and it was that Puritan's punishment to know that those that he cared for on Earth would do evil as he had done.

So, let's look at the clues that suggest that it was most likely never said.  For starters, there's the descrepency over who exactly said it.  The most common name attatched to it is Charles H. Duell, in which case the date given for the quote is 1899.  Alternatively, it's given to an unnamed "director" who resigned in 1875, an unnamed patent office clerk in 1833, or an unnamed employee of the British patent office (in which case, no date is given, other than a general date of sometime in the 19^th century).  Strike number one.

The most common source, as mentioned, appears to be Duell.  Which is a wonderful testament to the ability of misinformation to spread over the Internet.  Do a search, take a look at the Google page summarys that appear, and look at how many of them are exactly the same.  All those quote archives simply plagarise off of each other, without ever checking to see if the information they're copying is accurate.  (Which is much like all the various lyric databases.  If you find one song mislabelled in one of them, it's probably mislabelled in all of them.)

Of course, that's not saying it wasn't already well travelled before the Internet arrived.  It was apparently well enough known back in 1985 for President Reagan to use it in a speech to business leaders.  (I'll be polite and keep the snarky comments to myself.)  It's just that, what with the Internet, a search for information on Duell gets drowned out by the sheer amount of noise being put out by all these quote indexes.  But I digress….

Getting back on topic: the quote doesn't appear to match the tone of Duell's reports to President McKinley for the period during which he was Commissoner (1898 to 1901), in which he talks about the growing number of patents submitted each year and the need for America to foster innovation.  Or how about his opinion in his own words, taken from his 1900 report: "The world owes as much to inventors as to statesmen or warriors. […] Their labor-saving machinery does work that it would take millions of men using hand implements to perform. In this century the debt will be piled still higher, for inventors never rest."  Doesn't sound like someone who thinks that "Everything that can be invented has been invented", now does it?

So, that's it; I'm done.  For a fuller discussion check out the Skeptical Inquirer article A Patently False Myth Still!, from which I grabbed most of the info.
The Reagan quote can be found in the online papers available from the Ronald Reagan Presidential Library.  October 3, 1985: Remarks to Business Leaders in Cincinnati, Ohio.
The quotation from Duell's 1900 report comes from a post to the Patent Information Users Group mailing list.

Now, seeing as (according to a post on the Stumpers mailing list) this quote has been being debunked since at least 1945, could we please stop using it?

Next week: Bill Gates and 640K.

"This," said I, "is scarce less fragile or less frail than one of those delicate forgotten years." Then I took my wreath in my hand and went from here. And when I had come by paths of mystery to that romantic land, where the valley that rumour told of lies close to the mountainous moon, I searched among the grass for those poor slight years for whom I bought my sorrow and my wreath. And when I found there nothing in the grass I said: "Time has shattered them and swept them away and left not even any faint remains."

But looking upwards in the blaze of the moon I suddenly saw colossi sitting near, and towering up and blotting out the stars and filling the night with blackness; and at those idols' feet I saw praying and making obeisance kings and the days that are and all times and all cities and all nations and all their gods. Neither the smoke of incense nor of the sacrifice burning reached those colossal heads, they sat there not to be measured, not to be over-thrown, not to be worn away.

I said: "Who are those?"

One answered: "Alone the Immortals."

And I said sadly: "I came not to see dread gods, but I came to shed my tears and to offer flowers at the feet of certain little years that are dead and may not come again."

He answered me: "These are the years that are dead, alone the immortals; all years to be are Their children—They fashioned their smiles and their laughter; all earthly kings They have crowned, all gods They have created; all the events to be flow down from their feet like a river, the worlds are flying pebbles that They have already thrown, and Time and all his centuries behind him kneel there with bended crests in token of vassalage at Their potent feet."

And when I heard this I turned away with my wreath, and went back to my own land comforted.