ated phenomena appeared first, then chemical, then vital, and, lastly, rational (if these can be at all considered in the same category). It is also the order of dependence, and therefore, also, of historic development of the sciences based upon them. Mechanics is absolutely dependent on mathematics, and must, therefore, have awaited its development. Similarly, physics is dependent on both mathematics and mechanics, but especially the latter, and therefore must await its development. Similarly, chemistry must wait on all the preceding, but especially on physics; and biology must patiently await the development of all the preceding, but especially of chemistry.
But observe the following qualification: This is the necessary order in which these departments take on true scientific form, but not necessarily the order in which they are first commenced to be cultivated. Astronomy commenced to be cultivated by the Chaldeans long before mathematics or mechanics was sufficiently advanced to be applied to it. Biology commenced to be cultivated by Aristotle, or perhaps even by Solomon, long before chemistry and physics were sufficiently advanced to be of any use in biological investigations, add indeed before these sciences were born. In all sciences, but especially in the higher and more complex departments, there are three distinct stages of advance: The first consists in the observation, collection, and arrangement of facts—descriptive science. The second is the reduction of these to formal laws—formal science. Thus far the science is independent of other sciences. The third is the reference of these laws to the more general laws of a more fundamental science—in the hierarchy as their cause—causal science. It is this last change only which necessarily follows the order indicated above. Its effect is always to give great impulse to scientific advance; for then only does it take on the highest scientific form, then only does it become one of the hierarchy of sciences, and receives the aid of all. Thus to illustrate: Tycho-Brahe laboriously gathered and collated a vast number of facts concerning planetary motions—descriptive astronomy. Kepler reduced these to the three great and beautiful laws known by his name—formal astronomy. But it was reserved for Newton, by means of the theory of gravitation, to explain the Keplerian laws by referring them to the more general and more fundamental laws of mechanics as their cause, and thus he became the founder of physical or causal astronomy. In other words, astronomy was first a separate science based on its own facts. Newton connected it with mechanics, and thus made it one of the hierarchy. From that time astronomy advanced with increased rapidity and certainty. Astronomy first rose as a beautiful shaft, unconnected and unsupported, except on its own pediment. In the meantime, however, another more solid and more central shaft had grown up under the busy hands of many builders, viz., mechanics. Newton connected the astronomical shaft with the central column of mechanics, and thus formed a more solid basis for a yet higher shaft.
