I ought to mention that chapter iv. Of Book i. Has been reprinted (with considerable modifications) from the Contempo rary Review, in which it originally appeared as an article on Pleasure and Desire. And I cannot conclude without a tribute of thanks to my friend Mr. Venn, to whose kindness in accepting the somewhat laborious task of reading and criticising my work, both before and during its passage through the press, I am indebted for several improvements in my exposition.