Public and Private
This chapter shows that Newton developed a theory of refraction based on the chymical principle sulfur, which he described in the first edition Opticks (1704). It also finds that the seeds of this theory extend back to Newton's 1675 Hypothesis of Light, where he explicitly abandons the Sendivogian theory of an aerial niter that he had affirmed in Of Natures obvious laws. Newton replaced the aerial niter, which had accounted for phenomena ranging from combustion and respiration to the fertilization of the earth, with a growing reliance on sulfur. Although he had reasons of his own for making this shift, Newton was also influenced by parallel developments in European chymistry, a field that was rapidly moving toward what would eventually be known as phlogiston theory.