Mathematical essays [electronic resource] : being essays on vulgar and decimal arithmetic. Containing, Not only the practical Rules, but also the Reasons and Demonstrations of them; with so much of the Theory, and of universal Arithmetic or Algebra, as are necessary for the better understanding the Practice and Demonstrations. With a general preface, on the Usefulness of Mathematical Learning. By Benjamin Donn, Of Biddeford, Devon. Teacher of the Mathematics, and Natural Philosophy, on Newtonian Principles.