of revolution of any two planets and the cube of their mean distances from the sun. These laws, with the larger share of astronomical knowledge, only express the force of the first simple law. Some are ready to feel that a law, like that of gravitation, loses proof of design by its very breadth and interior necessity. We may at some time be able to show that this law of gravitation is not an ultimate fact, but is involved in deeper facts, precisely as it itself now carries with it so many secondary facts. This depth to which thought extends, this range of the first pregnant principle, are in themselves fitted to emphasize the priority of mind to matter. If matter offered itself to mind in all our cosmogony as simply inert, indifferent material, we might well affirm its ultimate independence. But when we find, and increasingly find as we more fully understand it, that laws, definite relations, forces working from the outset toward given results, belong to its simplest forms and compose its properties, we are assured that its primordial elements are only the first terms of intelligence. However deep we dig down, mind is deeper, and has fully begun its work on the foundations of the world.

When we are dealing with such energies as heat and light, mathematical relations still go with us, and give us, as terms of thought, our chief power of comprehension and use. A remarkable example of this is offered in the lines of the spectrum. These disclose to us, now by their fixed position, and now by their slight displacement, the elements of distant heavenly bodies, the condition of these