AND THE MICROSCOPE. 25 



the following result : in the actual world a multitude of 

 substances and forces exist in a continual round of meta- 

 morphoses ; when these come in contact with the nervous 

 fibres of our bodies, they alter their condition, and this 

 altered condition is the cause of the production of those 

 pictures of the world, which our mind itself executes. 

 This self-sustaining world makes the most lively impres- 

 sion on us when the exciting conditions are in relation 

 with the optic nerves, but even here we can most distinctly 

 prove that the world of our conceptions, though always 

 dependent on the world without, is never homogeneous or 

 identical with it. 



One more example may serve to render this clear, and 

 at the same time to bring us on our way to the subsequent 

 considerations. Undoubtedly the simplest condition which 

 we can imagine to exist in the external world is that of 

 substance, matter or whatever we please to call it, which 

 occupies a certain space. Therefore, to make our concep- 

 tion of the world agree at all with the actual world, we 

 must first of all know, how great the space is, and how 

 large a portion of the space the matter, for example a 

 rock, occupies. But we have no scale by which to esti- 

 mate the size of space and, therefore, no definite notion of 

 the size of the world. When we say : " this man is six 

 feet high," that only means, " in the world of our concep- 

 tions the conceived man is six times the height of the 

 conceived foot ;" it is but a comparison of two conceptions. 

 Thence naturally originate the questions: how long is a 

 foot, an inch, a line and so on ? and we can only answer 

 by comparison with other just as indefinite magnitudes. 

 We see at once that not even in the most simple case, 

 can we arrive at a knowledge of the actual world from the 

 play of our conceptions ; the whole of our ideas of magni- 



