[10] “The first great agent which the analysis of natural phenomena offers to our consideration, more frequently and prominently than any other, is force. Its effects are either, 1st, to counteract the exertion of opposing force, and thereby to maintain _equilibrium_; or, 2ndly, to produce _motion_ in matter, “Matter, or that whatever it be of which all the objects in nature which manifest themselves directly to our senses consist, presents us with two general qualities, which at first sight appear to stand in contradiction to each other--activity and inertness. Its activity is proved by its power of spontaneously setting other matter in motion, and of itself obeying their mutual impulse, and moving under the influence of its own and other force; inertness, in refusing to move unless obliged to do so by a force impressed externally, or mutually exerted between itself and other matter, and by persisting in its state of motion or rest unless disturbed by some external cause. Yet, in reality, this contradiction is only apparent. Force being the cause, and motion the effect produced by it on matter, to say that matter is inert, or has _inertia_, as it is termed, is only to say that the cause is expended in producing its effect, and that the same cause cannot (without renewal) produce double or triple its own proper effect. In this point of view, equilibrium may be conceived as a continual production of two opposite effects, each, undoing at every instant what the other has done,”?--See continuation of the argument in _Herschel’s Discourse on the Study of Natural Philosophy_, page 223. In the Edinburgh New Philosophical Journal, vol. xlv., will be found a paper by Dr Robert Brown--“_Of the sources of motions upon the Earth, and of the means by which they are sustained_,” which will well repay an attentive perusal, as pointing to a class of investigation of the highest order, and containing deductions of the most philosophic description. [11] Friction, it is well known, generates heat; by rapidly rubbing two sticks together, the Indian produces their ignition; heat and light being both manifested. Under every mechanical disturbance electrical changes can be detected, and the action of heat in the combustion of the wood is a chemical phenomenon. [12] Count Rumford’s experiment consisted in placing a mass of metal in a box of water at a known temperature, and, by employing a boring apparatus, ascertaining carefully the increase of heat after a given number of revolutions. He thus describes his most satisfactory experiment:--