Dr Brown, it is well known, departed from his predecessors at this point, and may here be considered as one of the ablest representatives of the _sensational_ school. He expended much ingenuity in his analysis of perception, though in our opinion with very little result. No one saw more distinctly than he, that sensation alone could never give us the idea of an external object, or of space, or any thing external to the mind. No one has more satisfactorily shown that the notion of an extended resisting body, supposed by many to be resolved into the sensations of touch, cannot be derived from this source alone, but must have some other origin than the pure sensation, which is a mere mental phenomenon or state of the consciousness. But he imagined he had overcome the difficulty by introducing to us a new sensation, the _muscular_, that which we experience when we move our limbs. What he could not derive from the old sense of touch, he thought himself able to deduce from the reasonings of the mind on this muscular sensation; but the same difficulties which he himself so lucidly set forth when treating upon touch, will be found to pursue him here also. This muscular sensation, like every other, is in itself a mere state of the consciousness, begins and ends in a mere pleasure or pain. That it terminates abruptly, and contrary to our volition, in a feeling of resistance, (as when our arm is arrested in its motion,) is saying nothing more than that one sensation gives place to another without our willing it; a statement which might be made in a thousand other cases of sensation with equal propriety. But the author shall explain his own theory.