Silhouette mathematics: (Extended analytic geometry)

In 1945 Dr. R, S. Underwood published the first In a series of papers in the American Mathematical Monthly on a subject he calls extended analytic geometry. This series, leading to a book entitled Silhouette Mathematics, lays the foundation for what may lead to a uniform classification of equations in n variables, especially quadratic equations In n variables. The papers in that series can be found in the American Mathematical Monthly, as follows: 52(1949) 253-262, 56(1949) 158-164, 59(1952) 453-460, and 61(1954) 525-542.