amount of calorific motion derived originally from the sun; and, at each point at which the mechanical motion is destroyed or diminished, it is the sun's heat which is restored." The following quotation, also, is interesting as illustrating another phase of this law: "The work performed by men and other animals is due to the transformed energy of food. This food is of vegetable origin and owes its energy to the solar rays. The energy of men and animals is, therefore, the transformed energy of the sun. Excepting the energy of the tides, the sun's rays are the source of all the forms of energy practically available. It has been estimated that the heat received by the earth from the sun each year would melt a layer of ice over the entire globe a hundred feet in thickness. This represents energy equal to one horse-power for each fifty square feet of surface."--Anthony and Brackett. From the above quotations, it will be seen that the principal and most familiar sources (or great storage batteries) of Energy, apparent to dwellers upon this planet, are (1) the Earth manifesting the Power of Gravitation; and (2) the Sun, manifesting solar heat. In Tyndall's illustration we see the force of the sun's Energy--heat--raising the water from the ocean, by evaporation (although aided by the earth's gravitation "pulling down" the heavier air, allowing the vapor to rise). Then we see the Force of Gravitation causes the condensed vapor to fall as rain or snow on the mountain-top--then causing the rain to run into little streams, and so on until the river is reached--then causing the river to start on its downward journey of over seven thousand feet--then causing it to plunge over the cascade; to turn the wheels that operated the machinery, and turned the millstone, and the crusher of the miner, and the saw-mill, and the milk-churn, and the cradle. And, as Tyndall might have added, had he lived a little later--in the running of the dynamo, which running, produced electricity, that in turn caused lights to burn; other machinery to run and manufacture things; stoves to cook; flat-irons to iron; automobiles and engines to run; and many other things along the lines of transmitting Energy, Force and Motion.