Luminousness, light, colour, sound, heat, cold, flavour, odour, are sensations,--each of the entire is traceable from the function of the senses to the sensorium: deduct these, there is nothing perceived or to perceive; by means of the senses, respectively, we have knowledge of each,--and by the senses exciting the brain are the whole produced, as sensible effects. Outward bodies can have nothing the same or similar to sensible effects; and therefore nothing of the whole belongs to matter or bodies, or to physical philosophy. To mechanical nature the whole would be useless; to sensitive beings only are they useful; to us they are substitutes for Nature's deficiency in these respects; and the whole present a convincing proof of the wise, the strict economy of the Great Architect in his works. The objection is unfounded, that the external object should be like the sensation, in order to produce such sensation. But where is there sound in musical string or in the metal of a bell to promote the sensation; or yellow in the snowdrop to promote the sensation of yellow, when the eyes are jaundiced or a stained lens is before them: the sensation of pain is not the effect of pain; it and pain are one. That which in health promotes the sensation known as sweet, promotes that of bitter in sickness; the object is the same, the sensation changeable. In reason it cannot be said that fire is like the sensation, or the latter should be burning hot in the brain, where it is excited; neither is any material thing outside of us like a sensation of the brain; nor does the sensation inform us of anything but itself, excepting that it has a remote external cause. The common show-box exhibits the same landscape picture under the different aspects of summer, autumn, winter, and spring, according to the stained lens before the eyes; the picture has not all these colours, nor any, it is a mere black and white print, in which the stained lenses make no alteration. Nothing can be like a sensation but a sensation. That the objects we perceive and their remote cause are distinct things, is proved by the perception being that of a coin of the half-crown size, when the eyes are directed to a shilling and a convex lens before the face; if the lens be red, yellow, or blue, so is the perceived object, which is not the white shilling. We are invisible to each other; what is imagined to be a man's appearance, may be described as, various sensations of different colours symmetrically arranged, and constituting a single optically-excited mental effect. Neither is it the likeness of the sitter that the canvass exhibits, but the excited perception within the sensorium of the limner; for the renewal of which it is that he directs his eyes so frequently to the sitter's face, which is invisible to the limner, although he feels certain that he sees every feature.