led a very large class of philosophers to ascribe every change in the universe, material or intellectual, not to the original _foresight_ and arrangement merely,--the irresistible evidence of which even the impiety, that professes to question it, _must_ secretly admit,--but to the direct operation of the Creator and Sovereign of the world,-- “The mighty Hand, That, ever busy, wheels the silent spheres, Works in the secret deep; shoots streaming thence The fair profusion that o'erspreads the spring; Flings from the sun direct the flaming day; Feeds every creature; hurls the tempest forth; And, as on earth this grateful change revolves, With transport touches all the springs of life.” So prone is the mind to complicate every phenomenon, by the insertion of imagined causes, in the simple sequences of physical events, that one hypothesis may often be said to involve in it many other hypotheses, invented for the explanation of that very phenomenon, which is adduced in explanation of another phenomenon, as simple as itself. The production of muscular motion by the will, which is the source of the hypothesis of direct spiritual agency, in every production of motion, or change, in the universe, has itself given occasion to innumerable speculations of this kind. Indeed, on no subject has the imagination been more fruitful of fancies, that have been strangely given to the world under the name of philosophy. Though you cannot be supposed to be acquainted with the minute nomenclature of anatomy, you yet all know, that there are parts termed _muscles_, and other parts termed _nerves_, and that it is by the contraction of our muscles that our limbs are moved. The nerves, distributing to the different muscles, are evidently instrumental to their contraction; since the destruction of the nerve puts an end to the voluntary contraction of the muscle, and consequently to the apparent motion of the limb. But what is the influence that is propagated along the nerve, and in what manner is it propagated? For explaining this most familiar of all phenomena, there is scarcely any class of phenomena in nature, to the _analogy_ of which recourse has not been had,--the vibration of musical chords,--the coiling or uncoiling of springs,--the motion of elastic fluids, electricity, magnetism, galvanism;--and the result of so many hypotheses,--after all the labour of striving to adapt them to the phenomena, and the still greater labour of striving to prove them exactly adapted, when they were far from being so--has been the return to the _simple fact_, that muscular motion follows a certain state of the nerve;--in the same manner, as the result of all the similar labour, that has been employed to account, as it has been termed, for gravitation, has been a return to the simple fact, that, at all visible distances observed, the bodies in nature tend toward each other.