Historian and populariser of evolutionary science. Influenced by Auguste Comte and Herbert Spencer. Graduated from Harvard University in 1863. Gave a series of lectures on positive philosophy at Harvard, 1869–70. Assistant librarian, Harvard, 1872–9. Travelled to England in 1873. Published Outlines of cosmic philosophy (1874). Freelance lecturer and writer, 1879–88; retained by Houghton Mifflin Company from 1888. Wrote extensively on American history and politics.