The history of Science presents facts of the same meaning at every step. Indeed the integration of groups of like entities and like relations, may be said to constitute the most conspicuous part of scientific progress. A glance at the classificatory sciences, shows us not only that the confused aggregations which the vulgar make of natural objects, are differentiated into groups that are respectively more homogeneous, but also that these groups are gradually rendered complete and compact. While, instead of considering all marine creatures as fish, shell-fish, and jelly-fish, Zoology establishes divisions and sub-divisions under the heads _Vertebrata_, _Annulosa_, _Mollusca_, &c.—while in place of the wide and vague assemblage popularly described as “creeping things,” it makes the specific classes _Annelida_, _Myriopoda_, _Insecta_, _Arachnida_; it at the same time gives to these an increasing consolidation. The several orders and genera of which each consists, are arranged according to their affinities and bound together under common definitions; at the same time that, by extended observation and rigorous criticism, the previously unknown and undetermined forms are integrated with their respective congeners. Nor is the same process less clearly manifested in those sciences which have for their subject-matter, not classified objects, but classified relations. Under one of its chief aspects, the advance of Science is the advance of generalization; and generalization is the uniting into groups all like co-existencies and sequences among phenomena. Not only, however, does the colligation of a number of concrete relations into a generalization of the lowest order, exemplify the principle enunciated; but it is again and again exemplified in the colligation of these lowest generalizations into higher ones, and these into still higher ones. Year by year are established certain connexions among orders of phenomena that seem wholly unallied; and these connexions, multiplying and strengthening, gradually bring the seemingly unallied orders under a common bond. When, for example, Humboldt quotes the saying of the Swiss—“it is going to rain because we hear the murmur of the torrents nearer,”—when he remarks the relation between this and an observation of his own, that the cataracts of the Orinoco are heard at a greater distance by night than by day—when he notes the essential parallelism existing between these facts and the fact that the unusual visibility of remote objects is also an indication of coming rain—and when he points out that the common cause of these variations is the smaller hindrance offered to the passage of both light and sound, by media which are comparatively homogeneous, either in temperature or hygrometric state; he helps in bringing under one generalization the phenomena of light and those of sound. Experiment having shown that these conform to like laws of reflection and refraction, the conclusion that they are both produced by