identity is complete, and this results from the grand generalisation of recent times, that force, and heat is but a form of force, is indestructible, just as matter is indestructible. God has created a certain amount of force, as well as of matter, in the universe, and it is inconceivable that either should ever bo lessened in amount, except by a miraculous act of annihilation. This generalisation now looks like a truism j but how strano-e is it, that the human mind should arrive at it only in very recent times. But so it is in the whole history of human thought. The inscrutable mystery of one period is the self-evident axiom of another.
Another source of power of which we avail ourselves is the fall of water. We plant our mills on the banks of a stream, and the descent of the water turns the wheel. We do not readily think of the impalpable rays of the sun turning the spokes of the wheel; and yet the connexion is easily traced. The rays elevate the water in the form of vapour from one level to a higher; the vapour is deposited in the form of rain; the rain accumulates in the river; the river fills the buckets of the wheel, and through the operation of the wheel, the heat of the sun is converted into useful, industrial work; and this is done as really as if the rays turned round directly the spokes of the wheel.
It may be said that there is one kind of power at least which cannot possibly be traced to the sun—viz., animal power. The horse in harness, or the
