2O0 NATURE AND MAN. 



sense-perceptions which its presence has called up in his mind. 

 Thus when I press my hand against this table, I recognize its un- 

 yieldingness through the conjoint medium of my sense of touch, 

 my muscular sense, and my mental sense of effort, to which it will 

 be convenient to give the general designation of the tactile sense ; 

 and I attribute to that table a hardness which resists the effort I 

 make to press my hand into its substance, whilst I also recognize 

 the fact that the force I have employed is not sufficient to move 

 its mass. But I press my hand against a lump of dough; and 

 finding that its substance yields under my pressure, I call it soft. 

 Or again, I press my hand against this desk ; and I find that 

 although I do not thereby change \isform, I change \\.s place ; and 

 so I get the tactile idea of motion. Again, by the impressions 

 received through the same sensorial apparatus, when I lift this 

 book in my hand, I am led to attach to it the notion oi 7v eight or 

 ponderosity ; and by lifting different solids of about the same size, 

 I am enabled, by the different degrees of exertion I find myself 

 obliged to make in order to sustain them, to distinguish some of 

 them as light, and others as heavy. Through the medium of 

 another set of sense-perceptions which some regard as belonging 

 to a different category, we distinguish between bodies that feel 

 " hot " and those that feel " cold ; " and in this manner we arrive 

 at the notion of differences of temperature. And it is through the 

 medium of our tactile sense, without any aid from vision, that we 

 first gain the idea of solid form, or the three dimensions of space. 



Again, by the extension of our tactile experiences, we acquire 

 the notion oi liquids, as forms of matter yielding readily to pressure, 

 but possessing a sensible weight which may equal that of solids : 

 and of air, whose resisting power is much slighter, and whose 

 weight is so small that it can only be made sensible by artificial 

 means. Thus, then, we arrive at the notions of resistance and of 

 weight as properties common to all forms of matter ; and now that 

 we have got rid of that idea of light and heat, electricity and 

 magnetism, as " imponderable fluids," which used to vex our souls 

 in our scientific childhood, and of which the popular term " electric 

 fluid " is a " survival," we accept these properties as affording the 

 practical distinction between the " material" and the " immaterial." 



Turning, now, to that other great portal of sensation, the 



