Ross H E, Ross G M, 1976, "Did Ptolemy understand the moon illusion?" Perception 5(4) 377 – 385
Download citation data in RIS format
Did Ptolemy understand the moon illusion?
Helen E Ross, George M Ross
Received 30 January 1976
Abstract. Ptolemy is often wrongly credited with an explanation of the moon illusion based on the size-distance invariance principle. This paper elucidates the two Ptolemaic accounts: one in the Almagest, based on atmospheric refraction, and the other in the Optics, based on the difficulty of looking upwards. It is the latter passage which has been thought to refer to size-distance invariance, but it is more probable that it refers to the idea that the visual rays are diminished by the force of gravity (i.e. that the retinal image is reduced in size). Alhazen was probably the first author to explain the illusion by the size-distance invariance principle, and Roger Bacon the first to explain the enlarged apparent distance of the horizon by the presence of intervening objects. Delia Porta was the first to credit Ptolemy with these explanations, and this mistake was repeated by many subsequent authors.
Full-text PDF size: 1350 Kb
Your computer (IP address: 22.214.171.124) 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).