## Articles

*string theory*have nudged their way into public consciousness. It's a theory of everything in which everything's made of strings — or something like that. But why strings? What do they do? Where did the idea come from and why do we need such a theory?

**David Berman**has an equation-free introduction for beginners.

**Chris Sangwin**tells you how to make your own set of

*Napier's bones*and perform mathemagic with an interactive checker board.

**Phil Wilson**continues our series on the life and work of Leonhard Euler, who would have turned 300 this year. This article looks at the calculus of variations and a mysterious law of nature that has caused some scientists to reach out for god.

**Abigail Kirk**explores one of the formulae that carry his name.

**Tom Körner**'s explanation really is a piece of cake, served up with a hefty estimate of pi.

**Shahn Majid**met up with

*Plus*to explain.

**Caroline Series**and

**David Wright**give a short introduction to the maths behind their beautiful images.