own to shame, while they are at the same time forming a school of investigators. We do not grudge to Germany all the praise she well deserves, and the influence which the results of German research exercise on other nations is likely to urge them to such vigorous and determined efforts, that, sooner or later, science and every other progressive influence shall be "great gainers." Meantime, however, Germany is doubtless in the ascendant.
In the year 1845 appeared the first volume, and in 1846 the second, of Humboldt's "Cosmos." As comprising a view of the whole created universe depicted with the most wonderful sympathy, the book is as it were a canon forming a key to every thing that was known of Nature at the time. No man was then more suited for such work than was in the highest degree A. von Humboldt. A "Divina Commedia" of science, the "Cosmos" embraced the whole universe in its two spheres, heaven and earth. Under the leadership of the great searcher of Nature, as Dante once by the hand of Virgil, we climb from the depths of the universe, with its farthest nebulæ and double stars, down through the star depths to which belongs our solar system, to the air-and sea-enveloped earth, where form, temperature, and magnetic condition, are unveiled to us; then to the wealth of organic life, which, stimulated by the light, unfolds itself on its surface. It is an overwhelming picture of Nature, of surpassing beauty of outline, abounding in grand perspective, with the most careful execution of the smallest detail.
But we cannot conceal from ourselves that the "Cosmos," published twenty-five years ago, is in many of its parts now antiquated, not merely because it is wanting in many facts which have since been discovered, but most particularly because Humboldt was ignorant of some highly-important questions which have since taken their place in the foreground of scientific discussion, while our scheme of the universe during the last ten years has been considerably modified by the introduction of new and influential ideas. Any one, who to-day would attempt to recast the "Cosmos," must proceed like the Italian architect who took the pillars and blocks of the broken temples of antiquity, added new ones, and rebuilt the whole after a new plan.
There are three discoveries which, during the last quarter of a century, have entirely changed the position of natural science: the mechanical equivalent of heat, spectrum analysis, and the Darwinian theories.
Since, in the year 1842, an unknown physician in a Swabian country-town, Dr. Mayer, of Heilbronn, pointed out that a hammer 424 kilogrammes in weight, which falls from the height of a metre on an anvil, raises the heat of the latter by one degree centigrade, and that by this process of bringing a falling motion to a stand-still it is converted into a fixed quantity of heat—since then has science gained a new conception of the conditions of matter and of the powers of Na-
