of Physical Knowledge. 69 



hidden to the less trained eye and therefore remained con- 

 cealed. But ever the question arises : What is the significance 

 o£ this progress in fundamental conceptions for the satis- 

 faction of our thirst for knowledge ? Do we approach one 

 step nearer to a real knowledge of Nature by the refining 

 of our world image ? To this fundamental question let us 

 devote a brief consideration. It is not as if anything 

 essentially new could be said in this region, alread}- 

 traversed by manifold and endless speculation, but that 

 while on this point modern views are often diametrically 

 opposed, yet everyone who takes a deep interest in the real 

 aims of Science must necessarily take up some position. 



Thirty-five years ago, Hermann von Helmholtz in this 

 very place expounded the view that our perceptions never 

 give us an image of, but at most a message from, the external 

 world. For every attempt fails to demonstrate any kind of 

 similarity between the nature of the external impression and 

 the nature of the corresponding sensation ; all conceptions 

 which we make for ourselves of the external world only 

 reflect our own sensations in the last resort. Ts there any 

 sense, therefore, in opposing to our consciousness an inde- 

 pendent " intrinsic Nature w ? Are not indeed all so-called 

 " Laws of Nature u essentially but more or less effective 

 rules by means of which we summarize the temporal course 

 of our sensations as accurately and conveniently as possible ? 

 If that were so, then not only common-sense but exact 

 Science would have been fundamentally at fault from the 

 beginning. For it is impossible to deny that the whole 

 evolution of Physical knowledge up to now has aimed 

 towards the completest fundamental division between the 

 happenings of external Nature and the processes of human 

 perception. The way out of this embarrassing difficulty is 

 seen as soon as we go one step further along this line of 

 thought. Let us suppose that a Physical representation of 

 the Universe had been found which fulfils all our demands, 

 and therefore one that can completely and accurately repre- 

 sent all laws of Nature empirically known ; still that that 

 image even remotely resembles " real " Nature, can in no way 

 be proven. But this assertion has another side to it, which 

 is generally too little emphasized : for, in exactly the same 

 sense, the much bolder assertion that the proposed image 

 represents real Nature in all points with absolute fidelity 

 cannot be in any way refuted. For the first step in such a 

 disproof would be the ability to assert anything with certainty 

 concerning real Nature, and that, as everybody agrees, is 

 absolutely excluded. 



