_These Classes, how distinguished._--The class first named, are qualities of bodies as related to other bodies. The other class are qualities of bodies as related only to our nervous organization. The former all relate to bodies as occupying and moving in _space_, and come under the category of _resistance_. The latter relate to bodies only as capable of producing certain sensations in us. We may call the former _mechanical_, the latter _physiological_. _Connection of Sensation with the external Object._--From long habit of connecting the sensation with the external body which produces it, we find it difficult to persuade ourselves that taste and smell are mere affections of our senses, or that color is really and simply an affection of the optic nerve of the beholder, and that what is actually perceived in these instances is not properly a quality of the external object. A little reflection, however, will convince us that all which comes to our knowledge in these cases, all that we are properly cognizant of, is the affection of our own nervous organism, and that whatever may be the nature of the qualities in the object which are the producing cause of these sensations in us, they are to us occult and wholly unknown. _Power of producing these Sensations._--It is not to be denied, of course, that there is in external objects the power of producing these sensations in us, under given circumstances; but to what that power is owing, in what peculiarity of constitution or condition it consists, we know not. We have but one name, moreover, for the power of producing, and the effect produced. Thus the color, taste, smell, etc., of an object may denote either the sensation in us, or the unknown property of matter by virtue of which the sensation is awakened. It is only in the sense last mentioned, that the qualities under consideration may properly be called qualities of bodies. _Enumeration of the several Qualities as now classed._--According to the classification now made, the qualities of bodies may be thus enumerated. I. _Primary._--Extension, divisibility, size, density, figure, absolute incompressibility, mobility, situation. II. _Secondary._--A. _Objective_, or _mechanical_--as heavy or light, hard or soft, firm or fluid, rough or smooth, compressible or incompressible, resilient or irresilient, and any other qualities of this general nature resulting from attraction, repulsion, etc. B. _Subjective_ or _physiological_--as color, sound, flavor, savor, temperature, tactual sensation, and certain other affections of the senses of this nature. § IV.--ORGANS OF SENSE.--ANALYSIS OF THEIR SEVERAL FUNCTIONS