714
CURRENT TOPICS.
[J. F. I.
~Nomography. F.L. MARTINEAU and A. M. ARTER. (Proceedings of the Institution of Automobile Engineers, March, 1918. )-There is probably no device of mathematical analysis that has proved so great an aid to progress in every branch of technology as the graphic diagram in rectangular coSrdinates. Although other methods o,f graphically representing functions and variables have been developed, for th.e majority of applications the ~rectangular system, as may be judged by its widespread use, has proved preferable. W'orks on analytic geometry are generally restricted to a discussion of the rectangular and the extensively though less used polar systems. Among other methods of graphically representing variable quantiti.es that have been developed in recent years, the system known variously as "nomography," " alignment charts," and " parallel coordinates " has come into use, and is proving an important labor-saving device in graphic calculations better adapted to the purpose than the co6rdinate diagram.
This system is based upon the use of parallel axes upon which values of th.e variables are graduated. A simple form of a chart of this kind is represented by thermomete:r scales with adjacent graduations in Centigrade and Fahrenheit. With three variables there are three separate parallel lines. From these the required value of the function is determined by the intersection ,of a transversal passing through the two known values of the variables marked on the adjacent parallels. Under certain conditions one~ and sometimes all of th.ese lines become curved. The advantage of the nomographic diagram is apparent when a two-variable equation with a variable parameter is considered. With the rectangular system a series of curves must be constructed for different values of the parameter, and interpolations with such a diagram are uncertain. The nomogram, on the other hand, consists of only three graduated lines from which values are easily read or interpolated.