Cite as:
Ross H E, 2000, "Cleomedes (c. 1st century AD) on the celestial illusion, atmospheric enlargement, and size - distance invariance" Perception 29(7) 863 – 871
Download citation data in RIS format

Cleomedes (c. 1st century AD) on the celestial illusion, atmospheric enlargement, and size - distance invariance

Helen E Ross

Received 27 May 1999, in revised form 14 March 2000

Abstract. Cleomedes (Kleomedes) is a little-known Greek author (c. 1st century AD) who produced what is probably the earliest extant statement of size - distance invariance. He supported the Stoic philosophy and was concerned to discredit the Epicurean position that we perceive objects as having their true size. He explained the celestial illusion (the apparent enlargement of the sun near the horizon) in two ways: partly as a refractive effect of the atmosphere similar to angular enlargement when looking into water; and partly as a linear enlargement due to increased apparent distance in a misty atmosphere. He is the earliest extant author to offer apparent distance as a clear explanation of the celestial illusion. He attributed these views to Posidonius (c. 135 - 50 BC). His explanations remained at the geometrical level, and he did not speculate on sensory mechanisms.

Restricted material:

 Full-text PDF size: 267 Kb

 References  43 references, 1 with DOI links ()

Your computer (IP address: 50.16.17.90) has not been recognised as being on a network authorised to view the full text or references of this article. This content is part of our deep back archive. If you are a member of a university library that has a subscription to the journal, please contact your serials librarian (subscriptions information).