scripts to various essays-one to "The Constitution of the Sun," one to "The Philosophy of Style," one to "Railway Morals," one to "Prison Ethics," and one to "The Origin and Function of Music:" which last is about equal in length to the original essay. Changes have been made in many of the essays: in some cases by omitting passages and in other cases by including new ones. Especially the essay on "The Nebular Hypothesis" may be named as one which, though unchanged in essentials, has been much altered by additions and subtractions, and by bringing its statements up to date; so that it has been in large measure re-cast. Beyond these respects in which this final edition differs from preceding editions, it differs in having undergone a verification of its references and quotations, as well as a second verbal revision.

Naturally the fusion of three separate series of essays into one series, has made needful a general re-arrangement. Whether to follow the order of time or the order of subjects was a question which presented itself; and, as neither alternative promised satisfactory results, I eventually decided to compromise-to follow partly the one order and partly the other. The first volume is made up of essays in which the idea of evolution, general or special, is dominant. In the second volume essays dealing with philosophical questions, with abstract and concrete science, and with æsthetics, are brought together; but though all of them are tacitly evolutionary, their evolutionism is an incidental rather than a necessary trait. The ethical, political, and social essays composing the third volume, though mostly written from the evolution point of view, have for their more immediate purposes the enunciation of doctrines which are directly practical in their bearings. Meanwhile, within each volume the essays are arranged in order of time: not

indeed strictly, but so far as consists with the requirements of sub-classing.

Beyond the essays included in these three volumes, there remain several which I have not thought it well to include -in some cases because of their personal character, in other cases because of their relative unimportance, and in yet other cases because they would scarcely be understood in the absence of the arguments to which they are replies. But for the convenience of any who may wish to find them, I append their titles and places of publication. These are as follows:-" Retrogressive Religion," in The Nineteenth Century for July 1884; "Last Words about Agnosticism and the Religion of Humanity," in The Nineteenth Century for November 1884; a note to Prof. Cairns' Critique on the Study of Sociology, in The Fortnightly Review, for February 1875; "A Short Rejoinder" [to Mr. J. F. McLennan], Fortnightly Review, June 1877; "Prof. Goldwin Smith as a Critic," Contemporary Review, March 1882; "A Rejoinder to M. de Laveleye," Contemporary Review, April 1885.

LONDON, December, 1890.