Classical surveyors and astronomers, such as
Hipparchus, had specified the position of a place on the earth's
surface by the two " coordinates " latitude and longitude. Further,
historians have detected the idea of a graph as early as the 10th
century. But none of these contain the essence of Cartesian
geometry. This lies in representing curves or graphs by coordinates
connected by a formula.
While the 16th century had made progress in the
theory of equations, these had only been (as we should say) in one
variable. The idea of a relation of two current variables, of a
function, was in effect as new in algebra as was its application in
geometry. It was an idea, and an application, the unfolding of the
riches of which is still not finished ; and Descartes made only a
beginning. He stated, for instance, that if any curve could be
mechanically described, it could be represented by an equation. He
saw that the axes could be either perpendicular or oblique, but he
did not realise, as did Newton later, the immense usefulness of the
negative extensions of the axes.
The new method was not widely known until the
annotated edition of 1659. Wallis (1616-1703), however,
systematised and extended it, and took the step of identifying
cones with curves having equations of the second degree. This
clinched the classificatory primacy of degree both for equations
and for curves, and made it a natural step when Newton went on to
examine cubic curves.
Descartes taught that the language of nature is
mathematics and that 'nothing exists, except atoms and empty space;
everything else is opinions', His legacy was accepted by
Newton, who used, what we now call, Cartesian methods, to define a
world of matter in motion.
*
Fermat and Harriot had the idea, in a more cautious, less
suggestive, form at about the same time.