Note 83 — Chapter XXVIII · THEÆTETUS.

Mr. Campbell, in his Preface to the Theætêtus (p. lxxxiii.), while comparing the points in the dialogue with modern metaphysical views, observes. “Modern Experimental Science is equally distrustful of individual impressions of sense, but has found means of measuring the motions by which they are caused, through the effect of the same motions upon other things besides our senses. When the same wind is blowing one of us feels warm and another cold (Theætêt. p. 152), but the mercury of the thermometer tells the same tale to all. And though the individual consciousness remains the sole judge of the exact impression momentarily received by each person, yet we are certain that the sensation of heat and cold, like the expansion and contraction of the mercury, is in every case dependent on a universal law.”

It might seem from Mr. Campbell’s language (I do not imagine that he means it so) as if Modern Experimental Science had arrived at something more trustworthy than “individual impressions of sense”. But the expansion or contraction of the mercury are just as much facts of sense as the feeling of heat or cold; only they are facts of sense determinate and uniform to all, whereas the feeling of heat or cold is indeterminate and liable to differ with different persons. The certainty about “universal law governing the sensations of heat and cold,” was not at all felt in the days of Plato.