in this essay require modification in view of later work. These are indicated in footnotes. Its tone is partly explained by the fact that the editor begged me to make the article "as romantic as possible."
All the above essays are entirely popular, but those that follow are somewhat more technical. "On Scientific Method in Philosophy" was the Herbert Spencer lecture at Oxford in 1914, and was published by the Clarendon Press, which has kindly allowed me to include it in this collection. "The Ultimate Constituents of Matter" was an address to the Manchester Philosophical Society, early in 1915, and was published in the Monist in July of that year. The essay on "The Relation of Sense-data to Physics" was written in January, 1914, and first appeared in No. 4 of that year's volume of Scientia, an International Review of Scientific Synthesis, edited by M. Eugenio Rignano, published monthly by Messrs. Williams and Norgate, London, Nicola Zanichelli, Bologna, and Félix Alcan, Paris. The essay "On the Notion of Cause" was the presidential address to the Aristotelian Society in November, 1912, and was published in their Proceedings for 1912-13. "Knowledge by Acquaintance and Knowledge by Description" was also a paper read before the Aristotelian Society, and published in their Proceedings for 1910-11.
London,
September, 1917
