[7] “Natural Groups given by Type, not by Definition.... The class is steadily fixed, though not precisely limited; it is given, though not circumscribed; it is determined, not by a boundary-line without, but by a central point within; not by what it strictly excludes, but what it eminently includes; by an example, not by a precept; in short, instead of Definition we have a Type for our director.  A type is an example of any class, for instance, a species of a genus, which is considered as eminently possessing the characters of the class.  All the species which have a greater affinity with this type-species than with any others, form the genus, and are ranged about it, deviating from it in various directions and different degrees.”—­WHEWELL, The Philosophy of the Inductive Sciences, vol. i. pp. 476, 477.

[8] Save for the pleasure of doing so, I need hardly point out my obligations to Mr. J.S.  Mill’s “System of Logic,” in this view of scientific method.

VI.

ON THE STUDY OF ZOOLOGY.

Natural history is the name familiarly applied to the study of the properties of such natural bodies as minerals, plants, and animals; the sciences which embody the knowledge man has acquired upon these subjects are commonly termed Natural Sciences, in contradistinction to other, so-called “physical,” sciences; and those who devote themselves especially to the pursuit of such sciences have been, and are, commonly termed “Naturalists.”

Linnaeus was a naturalist in this wide sense, and his “Systema Naturae” was a work upon natural history, in the broadest acceptation of the term; in it, that great methodizing spirit embodied all that was known in his time of the distinctive characters of minerals, animals, and plants.  But the enormous stimulus which Linnaeus gave to the investigation of nature soon rendered it impossible that any one man should write another “Systema Naturae,” and extremely difficult for any one to become a naturalist such as Linnaeus was.

Great as have been the advances made by all the three branches of science, of old included under the title of natural history, there can be no doubt that zoology and botany have grown in an enormously greater ratio than mineralogy; and hence, as I suppose, the name of “natural history” has gradually become more and more definitely attached to these prominent divisions of the subject, and by “naturalist” people have meant more and more distinctly to imply a student of the structure and functions of living beings.

However this may be, it is certain that the advance of knowledge has gradually widened the distance between mineralogy and its old associates, while it has drawn zoology and botany closer together; so that of late years it has been found convenient (and indeed necessary) to associate the sciences which deal with vitality and all its phenomena under the common head of “biology;” and the biologists have come to repudiate any blood-relationship with their foster-brothers, the mineralogists.