A new poem by Percy Bysshe Shelley, whose admirers were beginning to worry that he was all played out after that bird thou never wert, has surfaced in England. So has a bunch of letters from George Gordon, Lord Byron, believed to be the only letters he ever wrote that were not read by more than a score of people besides the addressees. And in Boston, half the final draft of the Declaration of Independence has turned up in somebody's attic, proving conclusively that Thomas Jefferson knew that the opposite of "alienable" is not "unalienable," even if his printer didn't.

All this is great news not only for scholarly types desperately casting around for thesis topics, but for old readers. An old reader is not necessarily an aged one, but just talks that way - an old reader is a reader who only reads old books.

There are various motives for being an old reader, only one of which is the snobbery of not having read the latest book that everybody's talking about. Old books not only tend to be written in regular English, with plots and characters and other old-fashioned luxuries, but you don't have to wait for them to come out in paperback.

However, there are disadvantages in being one. The supply is limited. Old readers may have patience, but the wait for a new George Eliot novel has been tryingly long.

The Dickens, Thackery and Trollope buffs were comparatively lucky because they could read the complete works from beginning to end, and then start at the beginning again, because nobody's memory is that long. On the other hand, a Jane Austen addict has to be exceptionally loyal or exceptionally dotty to keep going on that method.

But the appearance of these old writings rouses hope. Perhaps somewhere there is a library full of new 19th-century books waiting for people who will appreciate them.

Of course the publishing industry must be aware of its market, and we cannot expect them to discover new old manuscripts for which there is no market. The Shelley poem may be a good test case. Before the senior editors and advertising people of any publishing house have their meeting, it would be helpful for them to know what the public demand is for a new Shelley poem. if it goes over, perhaps they could risk bringing out a new Keats volume.

It may be that the Declaration of Independence audience is exhausted from the Bicentennial, and there is no use discovering a Constitution with three hitherto unread clauses. Perhaps the budget should be spent in finding Civil War memorabilia, instead.

But surely, if they are convinced there are buyers for a possible book, the book will be produced. If only the Dickens people can get together with the Trollope people who can agree with the Thackery people just what it is we all want. And when the dust settles from that, there will be plenty of old papers lying around.