  Given closed Riemannian manifold $(M^n, g)$ of positive Ricci curvature
$Ricci(g) \geq (n-1)g$ we study isoperimetric regions on the spherical cone
over $M$. When $g$ is Einstein we use this to compute the Yamabe constant of
$(M \times {\bf R}, g + dt^2)$ and so to obtain lower bounds for the Yamabe
invariant of $M\times S^1$.
