By Mark Ward BBC News Online technology correspondent

Amazon has run into trouble from US authors who are annoyed at it selling second-hand books. But some readers are using the net to give away the books they have just finished.

The internet would have saved JR Hartley a lot of bother.

It was his search for a second-hand copy of a little-known book called Fly Fishing which lasted for 12 years from 1983, all in the course of advertising Yellow Pages.

Some modern secondhand books are worth more than others

As he was the author of the book in question, his task was an old media equivalent of typing his own name into a search engine to see what impact he had made on the world - something that would take more like 12 seconds than 12 years.

Especially if you know where to look. One of the best places to search is the Advanced Book Exchange that gives access to 35 million second-hand titles held in more than 10,000 bookshops throughout the world.

Finding Farson

The booksellers like it, too.

"It's absolutely brilliant," said Ed Maggs, managing director of Maggs Brothers, an antiquarian bookshop in Berkeley Square established in 1835.

Easy to find with the web

Mr Maggs said the net was the best thing to hit the second-hand book trade since the catalogue.

"It's rendered a whole class of books that were previously unfindable and unsellable, saleable again," he said.

Books that were hugely popular in their day, such as the 1930s best-seller The Way Of A Transgressor by Negley Farson, would be very hard to find were it not for the net.

But not only does the net make it easy to find obscure books, it allows booksellers to find buyers for titles that otherwise wouldn't be worth giving shelf space to.

Adrian Harrington, chairman of the Antiquarian Booksellers Association and owner of Harrington Books, said many shops now got 25% of their business via the net.

"We sell to people we will never hear from again but we also form relationships with some customers who come back again and again," he said.

Owner occupier

People are searching out books for many different reasons.

George's movements are being tracked online

Many parents or grandparents try to track down childhood favourites that they now want to inflict on their own offspring. Others are pursuing a hobby and want the definitive texts and still others have their interest piqued and want to know more.

Serious bibliophiles search out these books because borrowing the book from a library just won't do. To them it is the possession of the object that is important. It, and all the other books they own, says something about them, if only to themselves.

Text life

It's perhaps for this reason that the BookCrossing website has sprung up.

Like the Where's George? website that tracks the movements of some US dollar bills, BookCrossing traces the movements of treasured texts.

The site was started by a group of Kansas City website makers and encourages people to register books at the site, label them as such, and then set them free in the wide world by leaving them on trains, in coffee shops, airline seat pockets and park benches.

Those that find the books are encouraged to report the title's movements and say whether they liked the book or not.

Antiquarian adjectives

Bumped Chipped Foxed Sunned Cracked Started Cocked Shaken

It's the 21st Century equivalent of a message in a bottle, and it's proving popular. BookCrossings now has more than 2,000 members and many times that number of books registered and travelling the world. One member has herself registered 1,500 books.

Maybe the advent of BookCrossing and the upsurge of interest in second-hand books is not so surprising.

The net is at its best when it fosters communities and gives people a way to share the things that they couldn't before now, when it underscores our common humanity.

Books are one of the main ways we explore this, usually alone but with the aid of BookCrossing, in groups, too.

After all, books are not just words on a page; they are a glimpse inside ourselves, an aid to the understanding and we need more of that than ever before.