 The distinguishing feature of Fechner’s new metaphysics is his insistence that it is based upon experience alone rather than the a priori reasoning of the old Naturphilosophie. Accordingly, the basic principle of his philosophical atomism is that atoms are “limiting concepts” in the analysis of experience. This means that they represent the ultimate units of analysis hitherto, so that they involve no claim that the analysis is complete. Atoms must be defined strictly in relation to the empirically given; they are not points behind or beyond space and time but within it; but there is always the stipulation that however small they are represented to be is never enough (Atom: 132). They appear to our representation as the smallest visible and tangible points; yet they are are smaller than the smallest we can see and touch (Atom: 156). 