German-American scientist, philosopher, educator, and lawyer who influenced philosophic study by criticizing contemporary scientific findings interpreted from linguistic theories of nature. Although initially he advocated Hegelian ontology as evidenced in General Principles of the Philosophy of Nature (1848), he later stressed his “two-fold relativity” of physical and cognitive phenomena. He pointed out that, although contemporary scientists claimed to be anti-metaphysical, their theories were often infected with ontological and metaphysical assumptions.

After emigrating to Cincinnati (1839) to complete his education and after serving as professor of physical sciences and philosophy at Fordham University (1844–47), he practiced law in Cincinnati, eventually becoming a judge (1853–55); later he was an official evaluator of candidates for teaching positions (17 years) before his appointment in 1885 as Pres. Grover Cleveland's minister to Italy. After four years in Rome, he retired to Florence.

Stallo's other works include The Concepts and Theories of Modern Physics (1882) and Reben, Abhandlungen und Briefe (1893; “Vintage Offerings, Essays, and Letters”).