The Superconducting Super Collider, if it is built before the end of the century, will certainly be the largest scientific instrument in the world. But whether its circumference should be 100 miles, or a mere 50 miles, has been a bone of some contention. The design energy is not at issue: SSC is to be an ultra‐highenergy proton‐proton storage‐ring collider with countercirculating beams of 20‐TeV protons providing p–p collisions at 40 TeV in the center of mass. The radius of the gargantuan storage ring required to keep these protons going round in circles varies inversely as the strength of the superconducting bending magnets one chooses to make up the ring.