An Extract of a Letter of Dr. J. Wallis, to M. Hevelius, from Oxford, Decemb. 31. 1673. Gratulatory for His Organographia; And Particularly Concerning Divisions by Diagonals, Lately Inserted in Mr. Hook's Animadversions on the First Part of the Machina Coelestis of the Honourable Joh. Hevelius; But so Faultly Printed, That It Was Thought Fit, at the Author's Desire, in His Letter to the Publisher, of Januar. 4. 1674/5 to be here Done More Correctedly