|Sphere paperback, 1979. Cover painting by Peter Jones.|
"The Mathematics of Magic - it was the greatest discovery ever. Or so though Professor Harold Shea. With the proper equations he could instantly transport himself and his friend Reed Chalmers back - or sideways - in time to all the wondrous lands of ancient myth and legend.
But slips in time were a hazard. And Shea's magic didn't always work quite as he expected. A dragon spell might yield a hundred dragons - or, even worse, one tenth of a dragon. And the various imaginary lands he travelled to held countless dangers that even Shea's equations couldn't predict..."