There are two types of energy which may be designated as energy of motion and energy of position. With the first of these we are familiar. A falling weight or running stream possesses energy of motion; it is able to overcome resistance by reason of its weight and velocity. On the other hand, before the weight began to fall, while, as yet, it had no motion but was at rest, it had the power of doing work by reason of its elevated position with reference to the earth. When the water of the running stream was at rest in the lake among the hills it had a power of doing work, an energy, which was not possessed by the waters of the pond in the valley below. This energy or power results from its peculiar position. Energy of motion is called kinetic energy; energy of position is called potential energy.