Resistance between two vertices of a graph

Question

Suppose $G$ is a connected graph with each edge being replaced by a 1 ohm resistance. Let $u$ and $v$ be two vertices of $G$. Then the resistance between $u$ and $v$ is $\frac{\tau(G')}{\tau(G)}$, where $\tau(G)$ is the number of spanning trees in $G$ and $G'$ is the graph of $G$ with $u$ and $v$ collapsed into one vertex. I remember that this statement is correct, but cannot find any references. Does anybody can provide me a book or paper for the above statement?