"The calculus, as developed by Newton, could be used and was used by him for the solving of a great variety of mechanical and hydrodynamic problems. It immediately became the mathematical instrument for all understanding of variables and motion, and hence of all mechanical engineering, and remained almost the exclusive one until well into the present century. In a very real sense it was as much an instrument of the new science as the telescope."11

There was controversy on the point as to who exactly was the first person to discover the system of differential and integral calculus. Some say it was Newton; others would say it was the German, Leibniz. "The verdict of science is that the methods were invented independently, and that although Newton was the first inventor, a greater debt is owning to Leibniz for the superior facility and completeness of his method."14 What Newton and Leibniz were to do, was to invent a tool, the calculus, in order to come up with proofs for these answers as were formulated in their impressive and active brains. With such a mathematical tool as the calculus, Newton was able to calculate the mass of each of the planets; sun and earth included. He estimated that the earth's density was between five and six times that of water (the figure by scientists today is 5.5). A number of very brilliant men, down through the generations, have looked at Newton's work and have shook their heads: his work was "above the reach of human reason and experience."15