We stand here on the brink of a great deep. For wise ends the system of nature has been constructed upon a line intermediate between the extremes of sameness and diversity. If the measure of difference between classes and individuals had been much greater or much smaller than it is, the accumulation of knowledge would have been extremely difficult, or altogether impossible. It is by the combination of similarity and dissimilarity among sensible objects that science from its lowest to its highest measures becomes possible. If all animals, or all plants had been in their sensible qualities precisely the same, there would have been of animals or vegetables only one class: we could have had no knowledge regarding them, except as individuals: our knowledge would at this day have been less than that of savages. Again, if all animals or all plants had been in their sensible qualities wholly dissimilar--all from each, and each from all, it would have been impossible to frame classes; our knowledge, as on the opposite supposition, would have been limited to our observation of individuals. In either case Zoology or Botany would have been impossible. Man, endowed with intelligence, could not, in such a world, have found exercise for his faculties. It would have been like a seeing eye without a shining light. The power would have lain dormant for want of a suitable object. Ask the Botanist, the Naturalist, the Chemist--ask the votary of any science, what makes accumulated knowledge possible; he will tell you, it is the similarity which enables him to classify, accompanied by the diversity which enables him to distinguish. Wanting these two qualities in balanced union there could be no analogy; and wanting analogy, man could not be capable of occupying the place which has been assigned to him in creation.[1]