vi MYSTICISM AND LOGIC 



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 Felix Alcan, Paris. The essay "On the 

 Notion of Cause " was the presidential address to the 

 Aristotelian Society in November, 1912, and was pub- 

 lished in their Proceedings for 1912-13. " Knowledge by 

 Acquaintance and Knowledge by Description " was also 

 a paper read before the Aristotelian Society, and pub- 

 lished in their Proceedings for 1910-11. 



LONDON, 



September, 1917. 



