"An Introduction to Astronomy, Geography, Navigation and Other Mathematical Sciences" by Robert Morden 1702
What I found unusual about this textbook is that it still included a chapter on astrology. Apparently the rift between astronomy and astrology was not yet complete in Britain by the opening of the 18th century. Astrology had died out in the academic institutions of continental Europe during the 17th century but apparently it held on in Britain into the 18th century. This might have been one of the last astronomy textbooks to to include astrology. Other early 18th century textbooks, that were printed in Britain, such as those by John Keil, Charles Leadbetter, and David Gregory were pure astronomy.