Abstract
The early Greeks and Romans knew that the visual fields had definite limits, but one finds no exact figures prior to those of Venturi, who gives the vertical extent as 112° and the lateral as 135° The part in the books on optics written by Ptolemy (150 A. D.) containing the data given in the introductory quotation from Arago's work has been lost, and more exact information about his ideas on this phase of optics is not available. Euclid taught that a fluid streamed from the eye in the form of a cone with the point in the pupil and the base on the object looked at ; in other words, the base of the cone was the visual field. Helidore of Larisse described the base of this cone as circular. All inside this base was visible and all outside invisible. Astronomers and philosophers of all ages have made important
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