These _Propositions_ considered, there is no question relating to _Projects_, which, by the help of them, may not easily be Solved; and tho' it be true that most of them are to be met withal, in _Galileus_, _Torricellius_ and others, who have taken them from those Authors, yet their Books being Foreign, and not easy to come by, and their _Demonstrations_ long and difficult, I thought it not amiss to give the whole _Doctrine_ here in _English_, with such short _Analytical_ Proof of my own, as might be sufficient to evince their Truth. The Tenth _Proposition_ contains a _Problem_, untouch'd by _Torricellius_, which is of the greatest use in _Gunnery_, and for the sake of which this _Discourse_ was principally intended: It was first Solved by Mr. _Anderson_, in his Book of the Genuine Use and Effects of the _Gun_, Printed in the Year 1674; but his Solution required so much Calculation, that it put me upon search, whether it might not be done more easily, and thereupon in the Year 1678 I found out the Rule I now Publish, and from it the _Geometrical_ Construction: Since which time there has a large _Treatise_ of this Subject, Intituled, _L'Art dejetter les Bombes_, been Published by _Monsieur Blondel_, wherein he gives the Solutions of this _Problem_ by _Messieurs Buot_, _Romer_ and _de la Hire_: But none of them being the same with Mine, or, in my Opinion, more easy, and most of them more Operose, and besides mine finding the _Tangent_, which generally determines the _Angle_ better than its _Sine_, I thought my self obliged to Print it for the use of all such, as desire to be informed in the _Mathematical_ part of the Art of _Gunnery_.