In 1889, his oldest son, Ludwig, died of undiagnosed appendicitis. Along with the guilt that he felt for failing to recognize how serious his son's illness was, Ludwig Boltzmann also became increasingly isolated and insecure in his own department despite being one of the world's most eminent physicists. When a colleague secured a position for him at the University of Munich, Boltzmann gratefully accepted (although he was careful not to burn any bridges behind him when he left Austria). While he enjoyed his new work in Munich, the lack of any formal pension left him increasingly worried about what would happen to his family if he became disabled. This was a special concern for him due to his deteriorating eyesight. Although his wife regularly read scientific papers to him to spare his eyes, Boltzmann was terrified by the prospect of going blind completely. He also became homesick for Austria and eventually accepted a position at the University of Vienna in 1894 after years of waffling (the deciding factor was the prospect of complete pension in case he became disabled).
Despite international recognition (including an honorary degree from Oxford where he was revered), Boltzmann felt increasingly isolated in his native country. He traveled frequently and gave guest lectures across Europe and North America but was prone to intermittent episodes of depression. His frequent scientific arguments with other physicists (especially Ernst Mach) left him exhausted and he soon found himself in a new position at the University of Liepzig in 1900. It was shortly after arriving in Liepzig that he made his first suicide attempt and he officially retired a year later due to a stroke. While he was able to return to Vienna in 1902, the rumours concerning his mental health made the university uncomfortable and Boltzmann had to make a promise in writing that he would not attempt to leave Austria again.
By then, Ludwig Boltzmann's health problems severely impaired his ability to function as a lecturer. In addition to severe asthma attacks and poor eyesight (he hired an assistant to read all of his course material to him), he also experienced bad headaches and what appears to be angina episodes as well. These health issues didn't stop him from frequently working until early in the morning and travelling abroad giving lectures. His last lecture tour of the United States was in 1905 and the problems that Boltzmann was experiencing were readily apparent to his American colleagues. Not only was he plagued by repeated asthma attacks but his hosts at Berkeley were somewhat disgruntled by the odd manic behaviour that he was displaying. Still, he gave more than thirty lectures and newspaper reporters described his American tour as a triumphant success. Boltzmann was not so enthusiastic and he was openly disappointed that his lecture tour was not as successful as previous ones had been.
Shortly after returning from California, Ludwig Boltzmann committed suicide. Despite his chronic depression, his jovial description of his trip to California seemed enough to reassure friends and family that things were under control. Since he left no suicide note, his exact reason for killing himself remains unknown. Life managed to go on for Boltzmann's family and colleagues however. Although lectures in theoretical physics at his university were suspended for eighteen months after the suicide, Boltzmann's position was eventually filled by Friedrich Hasenohrl who dedicated his inaugural lecture to Ludwig Boltzmann and his research. Erwin Schrodinger and Ludwig Wittgenstein were particularly devastated by the great physicist's death since they had both been hoping to study with him. As for Henriette Boltzmann, she outlived her husband by more than thirty years before finally dying in 1938. Of all the Boltzmann children, it was Elsa, the daughter who discovered the body, who lived with the memory of her father's suicide the longest. Until her death in 1966, she steadfastly refused to talk about her reaction at finding her father's body.
While the usual caution about attempting to diagnose historical figures based solely on available accounts certainly applies here, the question of the exact nature of the psychiatric problem that Ludwig Boltzmann experienced still remains. In addition to the "neurasthenia" diagnosis he received during one of his repeated hospitalizations (a catch-all psychiatric label that was popular at the time), several biographers have speculated on the possibility that he suffered from bipolar disorder, primarily due to the apparent mood swings that he demonstrated at times. He often showed manic enthusiasm for his research work which could abruptly shift to deep depression. Even Boltzmann observed these mood swings and joked that they were due to his being born on the night between Mardi Gras and Ash Wednesday.
If he were diagnosed today, he would likely be considered to be suffering from late-onset bipolar disorder given that he was almost fifty when the first symptoms developed. The lack of any close relatives with psychiatric problems also reflect the possible late-onset diagnosis although, again, we will likely never know for certain. While never formally diagnosed, Ludwig Boltzmann is often listed among famous bipolar individuals. Whatever the diagnosis, Ludwig Boltzmann's life provides a fascinating example of the surprising ways in which scientific genius and mental illness can interact. Whether modern medical treatment would have enabled him to function longer is another question that can never be answered.
As a final postscript to Ludwig Boltzmann's saga, a commemorative plaque in his memory was mounted at the Hotel Ples on September 4, 2006 near the site where he committed suicide. It represents a sobering reminder of the death that rocked the scientific world so long ago.