James Patterson’s latest best seller, “The Angel Experiment,” has something unique, not in the sense of subject of the book but the way of it’s been marketed. It’s a four year old book and readers are mostly picking it up on the Kindle site at Amazon.com. The price? Very low, just $0.00.

James Patterson

James Patterson, the prolific and mega-selling author (and co-author) of numerous thrillers, says “I like the notion of introducing people to one book, while promoting the sales of another.”

His Kindle download is the first book of Patterson’s “Maximum Ride.” “We’ve given away thousands of free e-copies,” Patterson said. “`Maximum Ride’ is big already and we think it could be a lot bigger. That requires getting people to read it.”

Patterson is not alone. There are several other big brands, who are offering free e-books to the readers. The last few months, the top sellers on the Kindle include public domain titles such as “Pride and Prejudice” and “The Adventures of Sherlock Holmes,” and novels by Jennifer Stevenson and Greg Keyes. Their downloads have reached tens of thousands in recent few months.

The top three Kindle sellers, in the recent days, have been free books: Patterson’s, Joseph Finder’s “Paranoia” and Keyes’ “The Briar King.”

This is news strategy by book publishers and authors. There will always be someone who wants the free things. Publishers want to link such free things with the paid ones. Usually their strategy is to offer the first book in the series free for readers.

Scott Shannon, publisher of the Del Rey/Spectra imprint at Random House Inc., has something very interesting to share. Del Rey has had especially good luck with Naomi Novik’s “Temeraire” fantasy series. They offered the first book of the series for free. After that, the sales for the other Temeraire novels increased by more than 1,000 percent.

But offering a free book has some downsides. Readers may simply look for more free books rather than buying other books. Along with that, the electronic editions of new releases available at under $10 threatens to hamper the sales of from the more expensive hardcovers and may set an unrealistically low price for the future.

Publishers understand that they’re getting phenomenal success using free books to get more readers for other books, but in the long run, they have to guard the market. Offering free books is like an experiment and many publishers are focusing on the experiment.