order to what I have farther to write. And this may suffice for an
Introduction to Readers of quick Wit and good Understanding not yet
versed in Opticks: Although those who are already acquainted with this
Science, and have handled Glasses, will more readily apprehend what
followeth.

FOOTNOTES:

[A] In our Author's _Lectiones Opticæ_, Part I. Sect. IV. Prop 29, 30,

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