1879. Martineau, James. Essays. 2 vols. Trübner & Co., London.
1882. Michelet. Spencer's System der Philosophie. Spencer's Lehre von dem Unerkennbaren. Leipzig, 1891.
1898. Morgan, C. Lloyd. Mr Herbert Spencer's Biology. Natural Science, xiii. pp. 377-383.
1900. Pearson, K. The Grammar of Science, 2nd. Edition. A. & C. Black, London. Pp. 548.
1904. Pringle-Pattison, A. S. The Life and Philosophy of Herbert Spencer. The Quarterly Review, vol. 200, pp. 240-267.
1902. Sidgwick, Henry. Lectures on the Ethics of T. H. Green, Mr Herbert Spencer and J. Martineau. Macmillan & Co., London, Pp. 374.
1905. Sidgwick, Henry. The Philosophy of Mr Herbert Spencer. In "The Philosophy of Kant and other lectures." Macmillan & Co., London. Pp. 475.
1904. Sorley, W. R. The Ethics of Naturalism: a criticism, 2nd Edition, Blackwood, Edinburgh. Pp. 338.
1892. Sorley, W. R. Herbert Spencer. Article in Chambers's Encyclopædia.
1879. Sully, James. Article, "Evolution." Encyclopædia Britannica, ninth edition.