Oswald was born in Namur, Belgium. He graduated from Brussels University in 1865. He studied at Gottingen and Heidelberg where he obtained his M.A. and M.D. degrees. In 1866, as a military doctor he joined a corps of Belgian volunteers in support of Emperor Maximilian I of Mexico. He travelled in Mexico and later settled in the United States. Oswald was a conservationist. He was concerned about the negative effects of deforestation. He urged a legislative act to protect "the woods of all the upper ridges in hill countries." His writings on natural history experienced an extensive international readership. He wrote many scientific articles. His articles were published in the Popular Science magazine, The Monist journal, The Open Court journal and the North American Review. Oswald lived as a hermit and traveller, cooking his meals over an open fire. He was dubbed "the monkey man" as he had two or three pet monkeys that he allowed to move freely in his house. In 1905, his house including his monkeys were set on fire and destroyed.
Oswald was a freethought writer and naturalist who did not believe in the supernatural. Oswald has been described as an outspoken freethinker and one of the greatest advocates of the American freethought world. He authored the book The Secret of the East in 1883 and an article in 1891 that argued Christianity was of Buddhist origin. Lewis G. Janes suggested that this idea was "discredited at the outset by the totally different conceptions of the God idea and the destiny of man after death in the two religions." James Thompson Bixby wrote a rebuttal to Oswald's article. He argued that "the resemblances alleged by Dr. Oswald, even if granted, would be insufficient to prove his case... the differences between the Gospel and Buddhism run deeper and are more positive than the like-nesses." Edwin Arnold wrote that Oswald rejected the myths of Buddha and Christ for secular humanism, and that writers such as Oswald who wanted to "prove that Christianity was derived from Buddhism was a way of undermining its authority." Biblical scholars have rejected the theory that Christianity originated from Buddhism. Felix was influenced by the research of Rudolf Seydel. Orientalist Friedrich Max Müller rejected Oswald's thesis but respected his dedication to the subject. Müller commented that Felix was "one of the more conscientious and fair-minded students of Buddhism."
Death
Oswald died from a train crash at Syracuse, New York on September 27, 1906. Obituaries have described it as a tragic accident, whilst railway employees reported that he had committed suicide.
Selected publications
Oswald, F. L.. The Climatic Influence of Vegetation — A Plea for Our Forests. Popular Science Monthly 11: 385–390.