Among the scientists who have felt this need, and who have taken pains to fulfil it, the late Professor A. Eddington obtains an eminent position. Among his relevant utterances we will quote here the following, because it contains a concrete statement concerning the field of external observation which forms the basis for the modern scientific world-picture. In his Philosophy of Physical Science we find him stating that 'ideally, all our knowledge of the universe could have been reached by visual sensation alone - in fact by the simplest form of visual sensation, colourless and non-stereoscopic'.³ In other words, in order to obtain scientific cognition of the physical world, man has felt constrained to surrender the use of all his senses except the sense of sight, and to limit even the act of seeing to the use of a single, colour-blind eye.