Turning a sharp corner, he found himself in a huge chamber with a high, almost invisible ceiling.

I made myself understand, with some effort, that what I was seeing was actually happening on the other side of an invisible ceiling.

But the balloon had bumped up against an invisible ceiling of warm air and would not rise an inch.

Drifts of salt began to fall from the invisible ceiling.

Usually, though, he stared at the invisible ceiling and thought.

Art gazed at the invisible ceiling, tried to think, and at once drifted off.

The deterioration continued, with even the invisible ceiling growing cloudy and dark.

Then, with a shrug, she shouted at the invisible ceiling.

He rolled over in the darkness and stared at the invisible wooden ceiling.

I presumed the invisible ceiling was the same.