I. Bernard Cohen on Isaac Newton

“Opticks was out of harmony with the ideas of 19th-century physics. ...an exposition of the "wrong" (i.e., corpuscular) theory of light,—even though it also contained many of the basic principles of the "correct" (i.e., wave) theory. Not only had Newton erred in his choice... but also he apparently had found no insuperable difficulty in simultaneously embracing features of two opposing theories. ...by adopting a combination of the two theories at once, he had violated one of the major canons of 19th-century physics... Today our point of view is influenced by the theory of photons and matter waves, or the... complementarity of Neils Bohr; and we may read with a new interest Newtons ideas on the interaction of light and matter or his explanation of the corpuscular and undulatory aspects of light.”

“Of the many references to Newton in 18th-century electrical writings only a small number were to the Principia, the greater part by far were to the Opticks. This was true not alone of the electrical writings but also in other fields of experimental enquiry. ...[The Opticks] would allow the reader to roam, with great Newton as his guide, through the major unresolved problems of science and even the relation of the whole world of nature to Him who had created it. ...'''in the Opticks Newton did not adopt the motto... —''Hypotheses non fingo'''''; I frame no hypotheses—but, so to speak, let himself go, allowing his imagination full reign and by far exceeding the bounds of experimental evidence.”