Trained as an astronomer, he was appointed director of the Cincinnati (Ohio) Observatory in 1868. His interest gradually turned to meteorology, however, and he inaugurated a public weather service that served as a model for the national weather service, which was organized shortly thereafter as a branch of the Signal Service. In 1871 he was appointed chief meteorologist of the branch (which in 1891 was reorganized under civilian control as the U.S. Weather Bureau) and served in that capacity for more than 45 years.