Welcome to Oxford Index
A free discovery service, the Oxford Index lets you search across Oxford's digital academic content with a single click, and find related content every step of the way. Start here...
About Oxford Index Beta
16 indexed resources. Over 2 million items of content.
NEW: 300,000 trusted overview pages for answers at-a-glance
Media or press interested in reviewing the Oxford Index, please contact us for further information.
The Oxford Index Underbar
Jumpstart your research today
Quick Reference: A visual illusion of apparent movement created by gazing for a period of time at a fixed point in a waterfall and then looking at a stationary object, which appears to move upwards. The illusion was first discussed in print by the Greek philosopher Aristotle in the Parva Naturalia in the essay "On Dreams."