PREFACE.

Sixthly, I have all along applied theNewtonian Geometry , that is, the FluxionaryCalculus , for the Demonstrations, which Ithink is with the greatest Propriety and Just-ness in Physical Matters, because the Prin-ciples of this Geometry are in themselvesstrictly Philosophical, as I have shewn in itsproper Place Besides, the Process is notonly rendered by this means much morecongruous and natural, but more evidentand concise than by the common Methodsof Demonstration it could be. Of this wehave a signal Instance in the Calculation ofthe Angle, which the Incident Ray makeswilli the last refracted Ray in a Drop ofWater, as will appear by comparing whatis here contained in Scholium to Annot,CXXIV. with what you find on this Headin other Authors,

Seventhly, As the Bounds of thisScience have been of late Years vastly ex-tended, so I have been very careful to trea-sure up every useful Invention, and given ashort historical Account of the fame, andthe Names of the Authors. If in any ofthem I found an Improvement could bemade, 1 have done it, as in the Air-Pump ,

* See Vol. I. of Mathematical Institutions, justnow published in the General Magazine of Artsand Sciences.

the