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Book I.
$\scriptstyle {\underbrace {\quad \quad \quad } }$I have obſerved the ſame Proportion,The Proportion of the Magnitude of the Planets, in reſpect of one another, and the Sun. of their Diameters to that of the Sun, that I publiſhed to the World in my Book of The Appearances of Saturn: namely, the Diameter of the Ring round Saturn is to that of the Sun as 11 as to 37; that of Saturn himſelf about 5 to 37; that of Jupiter as 2 to 11; that of Mars as to 1 to 166; of the Earth as 1 to 111; and of Venus as 1 to 84: to which I ſhall now add that of Mercury obſerved by Hevelius in the Year 1661, but calculated by my ſelf, and found to be as 1 to 290.

If you would know the way that we came to this Knowledge of their Magnitudes, by knowing the Proportion of their Diſtances from the Sun, and the Meaſures of their Diameters, you may find it in the Book before mentioned: And I cannot yet ſee any Reaſon to make an Alteration in thoſe I then ſettled, altho’ I will not The Lamellæ more convenient than Micrometers.ſay they are without their Faults. For I can’t yet be of their Mind, who think the Uſe of Micrometers, as they call them, is beyond that of

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