consumption of coal Deed lead to no disquietude, at least in so far as there will be no diminution of oxygen in the atmosphere.
I have dealt thus at length with this illustration, because I wished through it to indicate to what false conclusions one-sided assumptions and problematic suppositions can lead. The problem in question here is much more complicated than is often supposed, even by prominent scientists, and to the objections which I have already urged against this doctrine of disaster very many more may be added, though it must be said that the matter was never taken very seriously in scientific circles.
In the impulsiveness of its youth, natural science has framed still many other one-sided suppositions when dabbling in strange territory. Thus Liebig ascribed the downfall of the world-embracing Roman Empire to the exhaustion of the soil, to the lack of phosphoric acid and potassium in the cultivated land, brought about by "robber farming," i.e., by too-continuous overcultivation of the soil. With propriety Du Bois- Reymond rejected this theory; but, on the other hand, the historian could not agree with this critic when he said: "Roman culture disappeared because it was built upon the quicksand of aesthetics and speculation." Du Bois-Reymond likewise attempted to solve a complicated phenomenon by too simple a formula.
Inadvertently we have just touched upon the relations of the natural sciences to the mental sciences, especially of history. For a long time these relations were very uncongenial, and insufficiency of knowledge and narrow conceptions upon both sides have often enough led to severe strife. The first attempts of naturalists to engage in the solution of historical problems from their point of view, and of historians—I recall here above all Buckle—to make use of natural history teachings in historical research, did not turn out well, and on that account could scarcely contribute toward an intellectual intercourse between the two "camps," as they were referred to frequently in those times of strife. It happened more frequently that these efforts suffered a severe rejection. So the saying was: "With the knife of the physiologist one may not cultivate the hard soil of history, but to that end is needed the strong plow of the historian." Or, an eminent historian relates that it had been made clear to him that history could not permit itself to be molested by Darwin and his associates.
An eminent historical investigator who once occupied this place of honor published very recently a work on genealogy. This, the author himself said, built the bridge between the historical and the natural sciences. In this work the effort is made to present systematically genealogy as learning in all its various relations to historical, social, political, judicial, and natural science questions.
The animal physiologists as well as those of botany have busied themselves not a little with the question of the determination of sex,
