A number of Classifications of human knowledge have been attempted, none of which were exact or complete, or could have been, for a reason which was stated above, and none of which are now considered to be satisfactory by the Scientific world. Bacon and D'Alembert, men of vigorous and vast intellectual capacity, were admirably adapted to such a work, so far as it could be performed in their day. But the state of knowledge and Scientific progress was not sufficiently advanced, at that time, to render any Classification which could be made of more than temporary value, and those furnished by these illustrious thinkers now appertain only to the archæology of Science.
The Classification of Auguste Comte, in the absence of a more exact, complete, and inclusive one, still holds the highest rank, and is the only one which now claims the attention of the general Thinker. It is very restricted in its application, professing to include only the domain which Comte calls abstract or general Science, which has for its object the discovery of the laws which regulate Phenomena in all conceivable cases within their domain, and excluding the sphere of what he denominates concrete, particular, or descriptive Science, whose function it is to apply these laws to the history of existing beings. This throws such Natural Sciences as Botany, Zoology, Mineralogy, Geology, etc., out of his range. He also excludes the domain of _practical_ Knowledge, comprising what is included under the terms, the Applied Sciences, the Arts, the Mechanical Sciences, etc. A Classification, far more detailed and comprehensive in its scope than anything yet published, is in preparation by Professor P. H. Vander Weyde, of the Cooper Institute--advanced sheets of which, so far as it is elaborated, have been kindly furnished to the writer by the author--the incomplete state of which, however, prevents a further consideration here.
The Principle which Comte adopted to guide him in his Classification was the following: 'All observable phenomena may be included within a very few natural categories, so arranged as that the study of each category may be grounded on the principal laws of the preceding, and serve as the basis of the next ensuing. This order is determined by the degree of simplicity, or, what comes to the same thing, of generality of their phenomena. Hence results their successive dependence, and the greater or lesser facility for being studied.' In accordance with this Principle, Comte establishes what he denominates the _Hierarchy of the Sciences_. Mathematics stands at the base of this, as being that Science whose Phenomena are the most general, the most simple, and the most abstract of all. Astronomy comes next, wherein the Static and Dynamic properties of the heavenly bodies complicate the nature of the investigation; in Physics, Phenomena must be considered in the midst of the still greater complications of Weight, Light, Heat, Sound, etc.; Chemistry has additional characteristics to trace in its subjects; Biology adds the intricacies of vital Phenomena to all below it; and Sociology, the sixth and last of Comte's Hierarchy--all other departments of thought other than those previously excluded from his survey, being regarded as out of the bounds of human cognition--deals with the still more complicated problem of the relations of men to each other in society.