It is evident not only in the general frame of Nature, that things most manifest unto sense, have proved obscure unto the understanding: But even in proper and appropriate Objects, wherein we affirm the sense cannot err, the faculties of reason most often fail us. Thus of colours in general, under whose gloss and vernish all things are seen, few or none have yet beheld the true nature; or positively set down their incontroulable causes. Which while some ascribe unto the mixture of the Elements, others to the graduality of Opacity and Light; they have left our endeavours to grope them out by twi-light, and by darkness almost to discover that whose existence is evidenced by Light. [SN: _The Principles of Colour according to the_ Chymists.] The _Chymists_ have laudably reduced their causes unto Sal, Sulphur, and Mercury; and had they made it out so well in this, as in the objects of smell and taste, their endeavours had been more acceptable: For whereas they refer Sapor unto Salt, and Odor unto Sulphur, they vary much concerning colour; some reducing it unto Mercury, some to Sulphur; others unto Salt. Wherein indeed the last conceit doth not oppress the former; and though Sulphur seem to carry the master-stroak, yet Salt may have a strong co-operation. For beside the fixed and terrestrious Salt, there is in natural bodies a _Sal niter_ referring unto Sulphur; there is also a volatile or Amnoniack Salt, retaining unto Mercury; by which Salts the colours of bodies are sensibly qualified, and receive degrees of lustre or obscurity, superficiality or profundity, fixation or volatility.