Letter: Wonder number more than a tool

Sir: It was heart-warming for those of us who work as mathematicians to read Charles Arthur's eulogy of the complex number i ("It may be square, but it's wondrous", 22 February).

But I imagine many were also surprised at his relegation of i to the status of a "tool we've made" - rather than a plain fact of nature like the number or the number 16. In spite of the historical terminology, i is no more (or less) imaginary than these "real" numbers.

And contrary to Mr Arthur's account, both i and its square-root-ness of -1 are quite easy to draw on a piece of paper: as a point in the plane midway in rotation about 0 between +1 and -1.

Dr WILLIAM OXBURY

Department of Mathematical Sciences

University of Durham