processes, will, I presume, easily allow me. And (Lastly) for as much as I have occasion more than once in my several Writings to treat either porposely or incidentally of matters relating to Colours; I did not, perhaps, conceive my self oblig'd, to deliver in one Treatise _all_ that I would say concerning that subject. But to conclude, by summing up what I would say concerning what I _have_ and what I _have not_ done, in the following Papers; I shall not (_on the one side_) deny, that considering that I pretended not to write an accurate Treatise of Colours, but an Occasional Essay to acquaint a private friend with what then occurrd to me of the things I had thought or try'd concerning them; I might presume I did enough for once, if I did clearly and faithfully set down, though not _all_ the Experiments I could, yet at least such a variety of them, that an attentive Reader that shall consider the Grounds on which they have been made, and the hints that are purposely (though dispersedly) couched in them, may easily _compound_ them, and otherwise _vary_ them, so as very much to increase their Number. And yet (_on the other side_) I am so sensible both of how much I have, either out of necessity or choice, left undone, and of the fruitfullness of the subject I have begun to handle; that though I had performed far more then 'tis like many Readers will judge I have, I should yet be very free to let them apply to my Attempts that of _Seneca_, where having spoken of the Study of Natures Mysteries, and Particularly of the Cause of Earth-Quakes, he subjoins.[1] _Nulla res consummata est dum incipit. Nec in hac tantum re omnium maxima ac involutissimá, in quâ etiam cum multum actum erit, omnis ætas, quod agat inveniet; sed in omni alio Negotio, longè semper à perfecto fuere Principia._ [1] L. Annæ Senecæ Natur. Quest. l. 6. c. 5. * * * * * _The Publisher to the_ READER. _Friendly Reader,_