Stationary, such airships would be heavier than air and so easier to park.

ECONOMIST: Monitor

Spills would also be a health risk, since carbon dioxide is heavier than air, and so can build up in low-lying or poorly ventilated spots.

ECONOMIST: Carbon capture and storage

What if a can of floor sealant mentioned the fellow who didn't realize that the fumes are heavier than air and can catch on a pilot light in the basement, and who died as a result?

FORBES

Air power enthusiasts had been making that claim continuously since the Wright Brothers proved the feasibility of heavier-than-air flight in 1903, so by the time the new millennium rolled around there were plenty of people in the Air Force ready to believe it.

FORBES: Air Force Positions For Resurgence In Pacific Era

But it is worth remembering that just over a century ago, heavier-than-air flight seemed an impossible dream.

ECONOMIST: Electric planes

Heavier-than-air flying machines are impossible!

FORBES: Protect yourself from the dangers of conventional wisdom!

However, partly because of the flip mechanism and the hidden components needed to make it work, the XPS 12 is heavier and thicker than the largest MacBook Air, which starts at the same price and has a bigger screen, at 13.3 inches.

WSJ: Review of Dell XPS 12: Dell Laptop Does Flips to Try to Be a Thick Tablet