The well-known writer of these scientific and critical essays, Prof. Ludwig Büchner, affords an exceptionally striking instance of the unenviable lot of some of our most popular writers of science. In one of these essays inscribed "Meine Philosophie," Professor Büchner has been compelled to defend the arduous work of his laborious life against a decidedly unfriendly and unappreciative criticism of his philosophy and whole scientific activity, that some time ago appeared in the American _Freidenker_ of Milwaukee. Prof. Büchner, with a touch of legitimate bitterness, repudiates the imputation of having been, or still being, as he himself calls it, only the "popularisator," expounder and commentator, of the theories and systems of other thinkers; that, on the contrary, in Germany and elsewhere, among the highest representatives of science, for more than thirty years Professor Büchner himself has been recognised and honored as an original worker and thinker. His book on "Force and Matter" (_Kraft und Stoff_) was published five years before Darwin's great work on the "Origin of Species." Subsequently his well-known popular Lectures in connection with Darwin's work claim the distinguished merit, of having more widely generalised and extended the Darwinian theory by embracing the origin and evolution of man, which had until then been overlooked by Darwin himself. By the contemporary press of Germany Professor Büchner was then charged with premature rashness, and with being only a shallow, imitative scientific dilettante; but all this vituperative criticism was for ever silenced, when in the year 1871 Darwin's own work appeared on the "Descent of Man," in which Darwin himself accepted all the consequences of the theory of evolution, as set forth in Professor Büchner's Lectures, and, somewhat later, in Professor Haeckel's "Natural History of Creation" (_Natürliche Schöpfungsgeschichte_). Professor Büchner, moreover, is the author of the widely popular work "The Future Life and Modern Science" (_Das künftige Leben und die moderne Wissenschaft_). To deny him, accordingly, the rank and merit of a solid and original scientist and thinker, as he himself says, is to do him a signal injustice, a positive injury.