Falling Water, Rising Rocks, 1834

Intrigued by an optical illusion he experienced while traveling in Scotland, Robert Addams wrote what is now considered one of the definitive observational accounts of so-called motion aftereffects.

Written byCatherine Offord

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One cloudy day in the early 1830s, Robert Addams, a traveling lecturer in chemistry and natural philosophy, found himself at the Falls of Foyers in Scotland, admiring the water of the River Foyers cascading down from the cliffs tens of meters above. Situated at the eastern shore of Loch Ness, the waterfall was a well-known beauty spot immortalized in the poems of Robert Burns.

It was here that Addams noticed a strange optical illusion. After staring a few seconds at the falling water, he moved his gaze to the rocks nearby and was surprised by the impression—albeit a fleeting one—that they were hurtling upwards. Intrigued, he put his experience into a letter to The London and Edinburgh Philosophical Magazine and Journal of Science that was published in 1834 as “An Account of a peculiar Optical Phænomenon seen after having looked at a moving Body, &c.”

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Meet the Author

Catherine Offord
After undergraduate research with spiders at the University of Oxford and graduate research with ants at Princeton University, Catherine left arthropods and academia to become a science journalist. She has worked in various guises at The Scientist since 2016. As Senior Editor, she wrote articles for the online and print publications, and edited the magazine’s Notebook, Careers, and Bio Business sections. She reports on subjects ranging from cellular and molecular biology to research misconduct and science policy. Find more of her work at her website.
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