'It generally takes the form of optical delusions.' "

It came about exactly as you said-- strange creatures, optical delusions, and everything.

The optical delusion, common to all lofty heights, raised the shores of the island, while the central portions appeared depressed.

Let us see if the mirror will conquer his optical delusions.

These momentary optical delusions are, I fancy, not uncommon.

Mahomet strained his eyes, but the blank was no optical delusion; neither Achmet nor his effects were there.

It's just an optical delusion.

He saw the small figure of the Goddess and he felt he was under an optical delusion.

This might have been an optical delusion, but it seemed to me that at each tick the box gave a little bound.

It was evidently just an optical delusion, aided by a good deal of credulity, and science could easily have explained the phenomenon.