to make out in some measure what I have at the beginning of this Essay either propos’d as my Design in this Tract, or deliver’d as my Conjectures concerning these matters.  And it not being my present Designe, as I have more than once Declar’d, to deliver any Positive Hypothesis or solemn Theory of Colours, but only to furnish You with some Experiments towards the framing of such a Theory; I shall add nothing to what I have said already, but a request that you would not be forward to think I have been mistaken in any thing I have deliver’d as matter of Fact concerning the changes of Colours, in case you should not every time you trye it, find it exactly to succeed.  For besides the Contingencies to which we have elsewhere shewn some other Experiments to be obnoxious, the omission or variation of a seemingly unconsiderable circumstance, may hinder the success of an Experiment, wherein no other fault has been committed.  Of which truth I shall only give you that single and almost obvious, but yet illustrious instance of the Art of Dying Scarlets, for though you should see every Ingredient that is us’d about it, though I should particularly inform You of the weight of each, and though you should be present at the kindling of the fire, and at the increasing and remitting of it, when ever the degree of Heat is to be alter’d, and though (in a word) you should see every thing done so particularly that you would scarce harbour the least doubt of your comprehending the whole Art:  Yet if I should not disclose to You, that the Vessels, that immediately contain the Tinging Ingredients, are to be made of or to be lin’d with Tin, You would never be able by all that I could tell you else (at-least, if the Famousest and Candidest Artificers do not strangely delude themselves) to bring your Tincture of Chochinele to Dye a perfect Scarlet.  So much depends upon the very Vessel, wherein the Tinging matters are boyl’d, and so great an Influence may an unheeded Circumstance have on the Success of Experiments concerning Colours.

* * * * *

FINIS.

* * * * *

A SHORT
ACCOUNT
OF SOME
OBSERVATIONS
Made by Mr. BOYLE

About a Diamond that Shines in the Dark.

First enclosed in a Letter written to
a Friend,

And now together with it annexed to the Foregoing
         Treatise, upon the score of the
                   Affinity Betwixt
                Light and Colours.

* * * * *

LONDON,

Printed for Henry Herringman. 1664

* * * * *

A COPY
OF THE
LETTER

That Mr. Boyle wrote to Sir Robert Morray,
to accompany the Observations touching
the Shining Diamond.

SIR,