Some of Harry Potter’s magic has rubbed off on Amazon.com.

The company, based in Seattle, announced today that its second quarter net income increased more than threefold, to $78 million, or 19 cents per share, compared with $22 million, or 5 cents per diluted share, in the same period last year.

Revenue increased 35 percent to $2.89 billion.

Amazon’s shares soared in after-hours trading. By early evening, they had increased 21 percent, to nearly $84. They had closed the regular session at $69.25 ahead of the earnings news, off $2.49 for the day, a decline of 3.5 percent.

The results come four days after Amazon.com delivered 2.2 million copies of “Harry Potter and the Deathly Hallows,” the final installment in the blockbuster fantasy trilogy. Amazon will count much of that revenue toward its bottom line next quarter, but other product purchases that Potter fans tacked on counted toward Amazon’s second quarter that ended on June 30.

Amazon beat Wall Street revenue estimates of $2.81 billion and its own forecasts of between $2.7 billion and $2.85 billion. Over the last three months, Amazon’s shares have risen around 60 percent, buoyed by anticipation of another healthy Harry Potter season, improved margins on its business and a slowdown in the growth of its technology investments.

“Our strong revenue growth this quarter was fueled by low prices and the added convenience of Amazon Prime,” Amazon’s founder and chief executive, Jeff Bezos, said in a written statement. “More and more customers are taking advantage of Amazon Prime and we’re pleased with the acceleration in subscriber growth this quarter.” Amazon Prime members pay $79 a year for unlimited express two-day shipping.

Scott Devitt, an analyst at Stifel, Nicolaus & Company, said that Wall Street has begun to reclassify Amazon as a technology company, like eBay and Google, instead of a comparatively low-margin retail company like Wal-Mart.

“Amazon was viewed as this low margin retail business, but it’s actually a company that will invest in its business and look out to the very long term at the expense of the short term,” he said. “Right now the company is reaping the reward of its investments over the last 12 or 18 months.”

Among its technology projects, Amazon’s Unbox movie download service allows users to buy or rent digital copies of some 10,000 films. Through a partnership with TiVo, Unbox customers who have TiVo digital video recorders can download those shows directly to their televisions.

In May, Amazon.com also said it would begin selling music digitally, in competition with competing services from Apple and Microsoft. But Amazon said it would not include the copy-protection software know as digital rights management, or D.R.M., which has frustrated some users because it creates confusion about the compatibility of downloaded songs with particular digital players.

Amazon has not yet provided an exact date for launching the service.