The physical world is generally a highly visible, and quite easily measurable source of information about one's self.

Light blazed up about his hand, an aura of brightness that had no visible source.

There was no visible source for the sound, but it sounded friendly.

I staggered under the impact of the blow from no visible source.

A visible source, for example, might be identified as a senior executive at the company in question.

Yet the air was bright, suffused with a soft light that had no visible source.

The subdued light that spread evenly over the entire dining room had no visible source.

It had no visible source and the water, when they plunged in, was icy cold.

Light seemed to flood the place from all angles, so that there were no visible sources.

What glittered in his eyes was a light with no visible source.