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LETTER I.
On the Colours of the Sapphire
and Turquoise.
SIR,
WHEN my Notes on Theophrastus were mentioned Yeſterday, ſome objected to the Sapphire's being coloured by Particles of Copper, and ſeemed very firm in the Opinion, that that Gem owes its Dye to a Native Zaffer.
I am ſorry I have only Room to name Things in thoſe Notes, without Opportunities of entering into a Detail of the Experiments. Thro' the Courſe of thoſe Notes I have not tied myſelf down to the Sentiments of any particular Author, but have, as my own Experiments and Obſervations directed, at Times agreed to, and in other Places diſſented from, the Opinions of the whole Number. And how I have ſucceeded in this Example, the faireſt Way of judging will be
firſt,
