PRE-EMINENCE AS A SCIENCE. 153 plishment. The perfection of a science is in exact proportion to its approach to this consummation; and, according to this test, astronomy distances all other sciences. Supposing it to relate to our solar system alone, the point is attained; for the single general law of gravitation comprehends the whole of its phenomena. It is to this that we must recur when we wish to show what we mean by the explanation of a phenomenon, without any inquiry into its first or final cause; and it is here that we learn the true character and conditions of scientific hypothesis,—no other science having applied this powerful instrument so extensively or so usefully. After having exhibited these great general properties of astronomical philosophy, I shall apply them to perfect the philosophical character of the other principal sciences. Regarding astronomical science, apart from its method, and with a view to the natural laws which it discloses, its pre-eminence is no less incontestable. I have always admired, as a stroke of philosophic genius, Newton's title of his treatise on Celestial Mechanics, The Mathematical Principles of Natural Philosophy;' for it would be impossible to indicate with a more energetic conciseness that the general laws of astronomical phenomena are the basis of all our real knowledge. Relation to other sciences. We may see at a glance that astronomy is independent of all the natural sciences, depending on Mathematics alone: and though, philosophically speaking, we put Mathematics at the head of the whole series, we practically regard it less as a natural science of itself (from the paucity of phenomena which it presents to observation) than as the repository of principles by which the natural sciences are interpreted and investigated. Philosophically speaking, astronomy depends on Mathematics alone, owing nothing to Physics, Chemistry, or Physiology, which were either undiscovered, or lost in theological and metaphysical confusion, while astronomy was a true science in the hands of the ancient geometers. But the phenomena of the other sciences are dependent, naturally as well as systematically, on astronomical facts, and can be perfectly studied only through astronomy. We cannot thoroughly understand any terrestrial phenomenon without considering what our globe is, and what part it bears in the solar system, as its situation and motions affect the conditions of everything upon it; and what would become of our physical, chemical, and physiological ideas, without consideration of the law of gravitation? In the remotest case of all, that of Social phenomena, it is certain that changes in the distance of the earth from the sun, and consequently in the duration of the year, in the obliquity of the ecliptic, etc., which in astronomy would merely modify some coefficients, would largely affect or completely destroy our social development. It is no exaggeration to say that Social physics would be an impossible science, if geometers had not shown us that the perturbations of our solar system can never be more than gradual and restricted oscillations round a mean condition which is invariable. If astronomical conditions were liable to indefinite variations, the human existence which depends upon them could never be reduced to laws. Not less important is the influence of astronomical science on our own intelligence. It has done much more than relieve us from superstitious terrors and absurd notions about comets and eclipses,-notions which, as Laplace observed, would spring up again immediately if our astronomy were forgotten. This science has done much more for our understandings than that. It has done more than any other pursuit--simply because it is the most scientific of all-to expose and destroy the doctrine of final causes, which is generally regarded by the moderns as the basis of every religious system, though it is in fact a consequence and not a cause. The knowledge of the motion of the earth has overthrown the very foundation of the doctrine, which supposed the universe to be subordinated to our globe, and therefore to Man. Since Newton's time, the development of celestial Mechanics has deprived theological philosophy of its principal intellectual office, by proving that the order maintained throughout our system and the whole universe is by the simple gravitation of its parts. If we took an à priori view, we should say that, as we exist, our system must be such as to admit of our existence; and one necessary condition of this is such a degree of stability in our system as we actually find. This TWO GREAT DIVISIONS OF THE SCIENCE. 155 stability we scientifically perceive to be a simple consequence of mechanical laws working among the incidents of our system, the extremely small planetary bodies in their relation to the larger sun; the small eccentricity of their orbits, and moderate inclination of their planes; which incidents, again, are necessary consequences of the mode of formation of the entire system. The stability by virtue of which we hold our existence is not found in the case of comets, whose perturbations are not only great, but liable to indefinite increase; and their being inhabited is inconceivable. Thus, the doctrine of final causes would be reduced to the truism that there are no inhabited bodies in our system but those which are habitable. This brings us back to the principle of the conditions of existence, which is the true positive transformation of the doctrine of final causes, and of far superior scope and profit in every way. Divisions of the science. Celestial We have next to consider the divisions of the science. These arise immediately out of the fact, now familiar to us, that astronomical phenomena are either geometrical or mechanical. They are Celestial Geometry, which is still called Astronomy, from its having possessed a scientific character before the other; and Celestial Mechanics, of which Newton was the immortal founder. Though our business is with our own system, the same division extends to Sidereal astronomy, supposing that kind of exploration to be within our power. As before, we see geometry to be more simple in its phenomena than mechanics, and that mechanics is dependent on geometry, without reciprocity. In fact, men were successfully inquiring into the forms and sizes of the heavenly bodies, and studying their geometrical laws, before anything was known of the forces which changed their positions. Whereas, the province of Celestial Mechanics is to analyse the motions of the stars, in order to refer them, by the rules of Rational Mechanics, to the elementary motions regulated by a universal and invariable mathematical law; thence, again, departing to perfect the knowledge of real motions by scientifically determining them à priori, taking from observation the Celestial necessary data-the fewest possible-for the calculations of general mechanics. This is the link by which astronomy and physics are connected, and connected so closely that some great phenomena render the transition almost insensible; as in the theory of the Tides. But it is evident that the whole reality of celestial mechanics consists in its having issued from the exact knowledge of true movements, furnished by celestial geometry. It was for want of this point of departure that all attempts before the time of Newton, even Descartes', however valuable in other ways, failed to establish systems of celestial mechanics. division of the science into two parts has therefore nothing arbitrary in it, nor even scholastic: it is derived from the nature of the science, and is at once historical and dogmatic. As for the subdivisions, we need not trouble ourselves with them now. This In regard to the point of view from which the science should be regarded, Lacaille thought it would simplify matters extremely to place his observer on the surface of the sun. And so it would, if the thing could be done in accordance with positive knowledge; but undoubtedly the solar station should be the ultimate and not the original one, under a rational system of astronomical study. And when, as in the case of this work, the object is the analysis of the scientific method, and the observation of the logical filiation of the leading scientific ideas, it matters less to obtain a clearer exposition of general results than to adhere to the positive method. I suppose my readers to be well acquainted with the two fundamental facts of the diurnal and annual rotation of our globe, as data without which nothing could be clearly understood of the essential methods and general results of astronomical science. I am not giving a treatise on astronomy, nor even a summary; but a series of philosophical considerations upon the different parts of the science, in which any extended special exposition would be misplaced. We must first see what methods of observation astronomers need, and are possessed of. CHAPTER II. METHODS OF STUDY OF ASTRONOMY. SECTION I INSTRUMENTS. ALL astronomical observation is, as we have seen, comprehended in the measure Observation. ment of times and of angles. The two considerations concerned in attaining the great perfection we have reached are the perfecting the instruments, and the application by theory of certain corrections, without which their precision would be misleading. Shadows. The observation of shadows was the first resource of astronomers, when the rectilinear propagation of light was established. Solar shadows, and also lunar, were very valuable in the beginning; and much was obtained from the simple device of a style, so fixed as to cast a shadow corresponding with the diurnal rotation to be observed: but the alterations rendered necessary by the annual motion, and impossible to make on that apparatus, rendered the instrument unfit for precise observations. Again, by comparing the length of the shadow cast by a vertical style with the height of the style, the corresponding angular distance of the sun from the zenith was computed and a valuable method this was: but the penumbra rendered the accurate measurement of the shadow impossible. The difficulty, aggravated by its unequal amount at different distances from the zenith, was partly removed by the use of very large gnomons; but not completely. These imperfections determined astronomers to get rid as soon as possible of the process of gnomonic measurement. Shadows will always be at hand to measure by when better means are wanting: and one application of this instru |