An Extract of a Letter from the Excellent Ronatus Franciseus Slufius, Canon of Liege and Counsellor to His Electoral Highness of Collen, Written to the Publisher in Order to be Communicated to the R. Society; Concerning His Short and Easie Method of Drawing Tangents to All Geometrical Curves without Any Labour of Calculation: Here Inserted in the Same Language, in Which It Was Written