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We were grateful to Jeremy Bernstein for his kind words about our book, Einstein's Mirror (THES, March 13), but we would like to correct a couple of points that he raised in his review. Both concern the book's major goal, which was not to create yet another biography of Einstein but to produce an accessible but accurate account of Einstein's theories of relativity. We do include some biographical material, but contrary to Bernstein's statement that Mileva Maric, Einstein's first wife, does not appear in our book, there is a picture of her with her husband and first legitimate child.

Discussing relativistic length contraction, Bernstein makes play of the fact that the George Gamov cartoons of a contracted Mr Tompkins got it wrong. He complains that we say things would not look "quite as simple" when "simple" is not the issue: "The images would not be contracted but rather rotated." This is puzzling, for on the same page we say "ordinary three-dimensional objects would appear rotated", and we illustrate this on the next page.

A popular book on a difficult scientific subject has to balance misleading over-simplification with overwhelming detail: we believe we have the balance about right.

Tony Hey and Patrick Walters. Department of electronics and computer science. University of Southampton