“The apparatus exhibited before the Association consisted of a brass paddle-wheel, working horizontally in a can of water. Motion could be communicated to this paddle by means of weights, pulleys, &c. The paddle moved with great resistance in the can of water, so that the weights (each of four pounds) descended at the slow rate of about one foot per second. The height of the pulleys from the ground was twelve yards, and consequently when the weights had descended through that distance they had to be wound up again in order to renew the motion of the paddle. After this operation had been repeated sixteen times, the increase of the temperature of the water was ascertained by means of a very sensible and accurate thermometer. “A series of nine experiments was performed in the above manner, and nine experiments were made in order to eliminate the cooling or heating effects of the atmosphere. After reducing the result to the capacity for heat of a pound of water, it appeared that for each degree of heat evolved by the friction of water, a mechanical power equal to that which can raise a weight of 890 lbs. to the height of one foot, had been expended. “Any of your readers who are so fortunate as to reside amid the romantic scenery of Wales or Scotland could, I doubt not, confirm my experiments by trying the temperature of the water at the top and at the bottom of a cascade. If my views be correct, a fall of 817 feet will of course generate one degree of heat, and the temperature of the river Niagara will be raised about one fifth of a degree by its fall of 160 feet.”--_Relation between Heat and Mechanical Power_: Philosoph. Mag. vol. xxvii. 1845. CHAPTER III. GRAVITATION. The Forms of Matter--Shape of the Earth--Probability of the Mass forming this Planet having existed in a Nebulous State--Zodiacal Lights--Comets--Volatilization of Solid Matter by Artificial means--The principle of Gravitation--Its Influence through Space and within the smallest Limits--Gravitating powers of the Planets--Density of the Earth--Certainty of Newton’s Law of the Inverse Square--Discovery of Neptune--State of a Body relieved from Gravitation--Experiment explaining Saturn’s Ring, &c.--General inference.