After the instrumentation was reset, Fermi told Weil to remove the rod another six inches. The pile was still subcritical. The intensity was increasing slowly - when suddenly there was a very loud crash! The safety rod, ZIP, had been automatically released. Its relay had been activated by an ionization chamber because the intensity had exceeded the arbitrary level at which it had been set. It was 11:30 a.m., and Fermi said, "I'm hungry. Let's go to lunch.

When the rods were pushed back in and the clicking had died down, we suddenly experiences a let-down feeling, for all of us understood the language of the counter. Even though we had anticipated the success of the experiment, its accomplishment had a deep impact on us. For some time we had known that we were about to unlock a giant; still we could not escape an eerie feeling when we had actually done it. We felt as, I presume, everyone feels who has done something that he knowns will have very far-reaching consequences which he cannot foresee.