The Relativity of Knowledge. 35 



relative to other senses, it is in rapid motion. On a rail- 

 road-train we have all observed how our motion-centres 

 have been agitated into a belief that we are moving, when 

 it is another train that moves, and not ours. As space and 

 motion are but forms of our own consciousness, having 

 some answering correspondence out of the consciousness 

 that produces them, so the tastes and odors, as well as the 

 colors and forms, of objects, are in the same condition of 

 relativity. If I look at a grain of sand through a magnify- 

 ing glass, I observe that what I see is magnified ; but the 

 grain itself does not change its size. If what I see is 

 made larger, but the thing itself is not made larger, the 

 conclusion is inevitable that I do not see the thing itself. 

 This is no trickery of logic, but unchallengeable reason. 

 With crossed fingers I feel one marble as two. I do not 

 actually feel two marbles, but two sensations proceeding 

 from one. If what I feel is doubled, and the thing itself 

 not doubled, I do not feel the thing itself. 



Take oxygen, hydrogen and carbon atoms. Arrange 

 them one way and you have oxalic, acetic, tartaric or citric 

 acids. Arrange them another way and you have sugar, 

 glucose or levulose. Arrange them other ways, and you 

 have tannin, or the various non-nitrogenous bitter princi- 

 ples of plants. Surely, the same thing cannot in itself be 

 sweet, sour and bitter. The various new arrangements 

 only enable it to tickle our nerve-centres in a somewhat 

 different manner. Turpentine, oil of lemon, oil of bergamot, 

 oil of orange, and oil of pepper, are not only composed of 

 the same kinds of atoms but in precisely the same propor- 

 tions. The shapes into which they are built enable them 

 to affect our nerve-centres differently. The scarlet and 

 yellow iodide of mercury vary only in the way each crys- 

 tallizes, and the color can be changed at will. (The lecturer 

 illustrated by exhibiting scarlet iodide of mercury on a 

 paper. Heating it over a lamp, it became yellow. Crush- 

 ing the yellow crystals with the hand, it again became 

 scarlet.) Salts of mercury, and iodine, may exist together 

 as perfectly transparent solutions, or as densely opaque 

 ones, according as they are able to affect our nerves. (Illus- 

 trated by experiment.) Cold substances brought togetlier 

 may produce heat. 



The relativity of all these properties appears plain after 

 a few such considerations as the following : Dissolve a 



