becomes such a figure as that of Fig. 357. The system may now be described in terms of the oblique axes X, Y; or may be directly referred to new rectangular co-ordinates öƒ, öñ by the simple transposition x =ã₤öƒã₤ãã₤öñã₤cotã₤ü, y =ã₤öñã₤cosecã₤ü.
(4) Yet another important class of deformations may be represented by the use of radial co-ordinates, in which one set of lines are represented as radiating from a point or ãfocus,ã while the other set are transformed into circular arcs cutting the radii orthogonally. These radial co-ordinates are especially applicable {731} to cases where there exists (either within or without the figure) some part which is supposed