Sir William Herschel conceived it to be the supreme object of astronomy ‘to obtain a knowledge of the construction of the heavens;’ and this, in his view, would be accomplished by the ‘determination of the real place of every celestial body in space.’ Thus limited, the problem would be completely solved could the absolute distance be ascertained of every object telescopically or photographically discernible in the sky. But even the attainment of this unattainable point would never have satisfied Herschel's restless spirit. The real scope of his inquiries went far beyond it. They had an historical, as well as a statistical aim. ‘Looking before and after,’ they embraced the past and future, no less than the present of the Cosmos.

Modern investigators are of the same mind. The heavens are regarded by them from a physiological, rather than from a purely anatomical point of view. Mere knowledge of structure, however accurate, will not content them. The vital functions of the organism, the mutual dependence of its parts, the balance of internal forces tending towards destruction and preservation, the dimly-apprehended aim of its divinely sustained activity, engage their eager attention. The heavens live and move, and the laws of their life and motion involve the material destiny of man. It is impossible that he should be indifferent to them.

Even, however, if our instinctive interest in the working of the machine were less keen, we should be driven to search out the dynamical relations of its parts by the impossibility of otherwise arriving at a true knowledge of their geometrical relations.