I N T R O D U C T I O N T O V O L U M E 1 6 l i x The couple returned to Berlin in early October. Einstein confessed that he was using the illness as “an invisibility cloak” so that he could ponder quietly and lay “foul eggs,” a reference to his new scientific theories (Doc. 298). Elsa also wrote that her husband had begun “to love his illness” and was shunning many responsi- bilities. He was doing much better, and was conscientiously following all of Lichtwitz’s instructions—taking the prescribed calcium diuretin pills regularly and doing breathing exercises and light calisthenics (Doc. 311). By late November, Einstein reported that his condition had improved considerably and that his physi- cian had allowed a return to a normal lifestyle. To ease his transition to life in the capital, Einstein intermittently spent portions of November and December in an empty chauffeur’s apartment in a manor owned by Plesch on the outskirts of Berlin, living alone like a “wild animal” (Docs. 321, 340). By January 1929, Einstein was again residing full time at the Haberlandstrasse apartment. Although his heart was doing better, his mobility was still very limited. In fact, he hardly set foot outside his home, not even for scientific events. But his earlier pessimism about his ability to resume traveling seemingly dissipated, and he now hoped to visit the Netherlands after he had recovered (Doc. 371). In early Feb- ruary, Einstein reported to Libman that both he and Elsa no longer suffered from any actual complaints, and confirmed the doctor’s theory that Berlin’s dry climate was better for heart patients than humid Scharbeutz (Doc. 398). In the ensuing months, Einstein continued to refrain from traveling, ostensibly since his health was still too fragile. For the same reason, he decided against visit- ing Eduard in Switzerland in March (Doc. 416). He similarly declined the invita- tion to accept an honorary doctorate from the Sorbonne, noting “the continuing fragility of my health that accompanies my heart problems.” According to the unanimous verdict of his doctors, he was “absolutely forbidden” from giving lec- tures to large audiences and from traveling in official capacity “for the rest of [his] life” (Doc. 417). The fact that his health was actually still unstable is confirmed by his confessing to Heinrich Zangger that the “slightest irregularity, too much talking or drinking, and the devil pops up and gives me a private admonition at night in- stead of letting me sleep.” This was possibly a reference to a recurrence of cardiac arrhythmia (Doc. 484). In May 1929, Einstein traveled to Brussels for the meetings of the scientific committee of the Solvay Congress, his first trip abroad since recovering. However, Elsa informed Paul Ehrenfest that visiting the Netherlands as well was out of the question since there would be “too much tension, excitement” (Doc. 533), thereby revealing the lingering repercussions of Einstein’s illness. Just how severe his