418 CBITICAL NOTICES : 150 pages, one may say that they are both perfect models of in- telligible exposition. Having the form of history, they are true in catching for the reader the essential idea which worked in each moment of the progress of the sciences concerned. This is especially noticeable in the sketch of the development of chemistry. There does not exist any other so complete, short and lucid account of the successive steps which chemistry has taken under the con- ceptions which are associated with the names of Dalton, Gay Lussac, Avogadro, Mitscherlich, Mendeleeff, etc., or of the essen- tial contributions of Clerk Maxwell, Pasteur, Joule and others to the atomic theory. So far as it is possible to judge, the same will be true of the chapter on astronomical theory ; it, like the other, is a remarkably clear essay. We have in these two chapters the exposition of the advance of exact measurement in relation to molar and to molecular masses. There are not wanting signs that the views of nature here described may be related to the other views in a scale of conceptions such as the philosopher may use for the unifying of science ; at present, however, we have just his- tory of science in which the successive working ideas are brought into admirable prominence. The eighty-five pages of the Introduction throw a clearer light on the author's intention than can be gained from the rest of this volume, which necessarily deals with only a very small part of his material. The immediate aim of the work is historical. It is the record, by a contemporary, of the general attitude of mind of the last generations, the features of which cannot be reconstructed from its works. ' It is the object of these volumes to fix, if possible, this possession ; to rescue from oblivion that which ap- pears to me to be our secret property ; in the last and dying hour of a remarkable age to throw the light upon the fading outlines of its mental life ; to try to trace them, and with the aid of all pos- sible information, gained from the written testimonies or the records of others, to work them into a coherent picture, which may give to those who follow some idea of the peculiar manner in which our age looked upon the world and life, how it intel- lectualised and spiritualised them.' Or, as the question of the book is presented later : ' What part has the inner world of Thought played in the history of our century what development, what progress, what gain has been the result of the external events and changes ? ' But such history has a deeper value than that of mere record. It is at least the preparation for the treat- ment of all human thought as an individual unity, and presup- poses that conception. It is not easy to fill the idea that the sum of human knowledge is an organic whole ; the encyclopaedic method reveals no unity, and the unity which is born of systematic formulation is barren ; the idea remains a conviction which seeks, and will some day find, a deeper expression. ' Unless I believed that our age was elaborating a deeper and more significant con- ception of this unity of all human interests, of the inner mental
