What [said Asa Gray] is the bright flame and vivid heat that is set free on your hearth when you kindle your piles of wood? It is the sunlight and sun-heat of a century ago. The beams were caught in the wilderness by the leaves of the trees; they were absorbed and stored in the trunks, and the light and heat day by day through many years was thus heaped up. When now combustion begins, it is simply a setting free of the radiance that was shed upon the forest many years ago. The noons of a time long past are making you comfortable in the wintry storm of the present. So when the anthracite glows in your grate, you feel the veritable sunbeams that were emitted aeons upon aeons ago upon the primeval world. It is the very light that was drunk in by those most ancient forests. It was held fast in the trunks, and when those faithful reservoirs in their turn were crushed and commingled and drenched until at last they lay under the earth as the coal beds, they nevertheless held fast this treasure. When you scratch your match you but unlock the hoard, and the sunlight of primeval days, diminished by no particle, glows and warms once more. This in substance was Asa Gray's introduction from which he went on to explain that in the progress of the universe no faintest throb of energy is lost. It might pass from form to form; heat might appear as a mode of motion, of weight, of elasticity, but no smallest unit perished. So the lecture flowed on into a luminous and comprehensive exposition of the great doctrine of the conservation and correlation of force. It was Asa Gray who brought us into touch with this new science just then announcing itself to the world. He was a co-worker and a compeer of the pioneers who at that moment were breaking a way for it, and it was our privilege to sit at the feet of a master.