examin’d.  Some Difficulties taken notice of in it.  What seems most likely to be the cause of colour:  that propriety is indeavoured to be shewn in a Glass ball:  that the reflection is not necessary to produce Colours nor a double refraction:  the Hypothesis further examined, both in the pellucid Medium and in the Eye.  The definitions of Colours; and a further explication and examination of the Proprieties of laminated Bodies; by what means they conduce to the production of Colours._

Observ. 10.  Of Metalline Colours.

That all Colours seem to be caus’d by refraction.  An Hypothesis_ consonant hereunto, explicated by Figures.  How several Experiments, of the sudden changing of Colours by Chymical Liquors may be hereby explicated:  how many wayes such Chymical Liquors may alter the colours of Bodies.  Objections made against this Hypothesis of two colours only, indeavoured to be answer’d, by several Reasons and Experiments.  The reason why some Colours are capable of being diluted, others not:  what those are:  that probably the particles of most metalline Colours are transparent; for this several Arguments and Observations are recited:  how Colours become incapable of diluting, explicated by a Similitude.  An Instrument, by which one and the same coloured Liquor at once exhibited all the degrees of colours between the palest yellow and deepest red:  as likewise another that exhibited all varieties of blues:  several Experiments try’d with these Boxes.  An Objection drawn from the nature of Painters colours answered:  that diluting and whitening a colour are different operations; as are deepening and blackening:  why some may be diluted by grinding, and some other by being tempered with Oyl:  several Experiments for the explicating of some former Assertions:  why Painters are forced to make use of many colours:  what those colours are:  and how mixt.  The conclusion, that most coloured Bodies seem to consist of transparent particles:  that all colours dissoluble in Liquors are capable of diluting:  some of mixing, what a strange variety may thereby be produc’d._

Observ. 11.  Of the Figures of Sand.

Of the substances and shapes of common and other Sands:  a description of a very small Shell.

Observ. 12.  Of Gravel in Urine.

A description of such Gravel, and some tryals made with it, and conjectures at its cause.

Obser. 13.  Of Diamonds in Flints.

A description and examination of some of them, explicated further by Cornish Diamonds:  several Observations about reflection and refraction:  and some deductions therefrom; as an explication of whiteness; that the Air has a stronger reflection then Water.  How several Bodies may be made transparent:  an explication of the Phaenomena_ of Oculus Mundi.  Of the regular Geometrical Figures of several Bodies:  an hypothetical explication mentioned:  the method of prosecuting this inquiry._