In 1834 he was appointed professor of physics at Leipzig. But in 1839, he injured his eyes in the research on afterimages by gazing at the sun through colored glasses, while studying the phenomena of color and vision, and, after much suffering, resigned. Subsequently, recovering, he turned to the study of the mind and its relations with the body, giving public lectures on the subjects dealt with in his books. Whilst lying in bed, Fechner had an insight into the relationship between mental sensations and material sensations. This insight proved to be significant in the development of psychology as there was now a quantitative relationship between the mental and physical worlds.