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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



doctrine of vision, is determined and changed. 

 Through this discovery we get definite knowledge 

 of the action of light within the human body it- 

 self, and we see that it is a quite peripheral organ 

 of the body, not at all the brain, but the eye, that 

 experiences this action. Furthermore, we learn 

 that this photographic process is not an intel- 

 lectual operation, but a chemical action performed 

 with the aid of certain vital processes; and that 

 in reality what we see is, not external objects, 

 but their images in the eye. We thus gain a new 

 analytical fact to aid us in understanding our 

 relations to the outer world, and in more sharply 

 distinguishing between the purely psychic and 

 the purely physical elements of vision. The re- 

 sult is a reconstruction, in part, of optics, and, at 

 the same time, of psychology. Chemistry now 

 steps in to investigate matters that heretofore it 

 had taken no cognizance of, namely, the highly- 

 important questions : " What is the retina-purple ? 

 What manner of substance is this ? How is it 

 formed, how decomposed, how reformed?" The 

 solution of these questions will not fail to open 

 an entirely new field of research ; and it is to be 

 hoped also that we shall soon witness new ad- 

 vances in technical photography — that we shall 

 be enabled to produce colored photographs. 

 Here, then, is an advance made simultaneously on 

 two different planes — progress both material and 

 intellectual. And thus it is that, with each real 

 advance in the knowledge of Nature, a series of 

 changes must of necessity take place not only in 

 the external but also in the internal relations of 

 man ; and no one can prevent the new knowledge 

 from affecting him. Each new fragment of real 

 knowledge has its effect on man, producing new 

 ideas, new trains of thought, and ultimately every 

 one finds himself compelled to consider even the 

 highest problems of mind in the light of natural 

 phenomena. 



But there are certain practical considerations 

 that concern us more nearly. Everywhere through- 

 out Germany we are now occupied in remodeling 

 our educational systems, enlarging and develop- 

 ing them and determining their forms. The new 

 Prussian education acts are on the threshold of 

 coming events. In all the German states larger 

 schoolhouses are being built, new educational 

 establishments founded, the universities enlarged, 

 high-schools and middle schools established. The 

 question arises : " What is to be the chief staple 

 of the instruction given ? What shall be the aim 

 of the school ? In what direction shall it work ? " 

 If natural science demands, and if for years we 

 ourselves have been striving to gain, an influence 



in the schools ; if we demand that natural science 

 shall be admitted into the schools in a larger 

 measure, and instilled into the minds of the 

 young, there to form the basis of new ideas, then 

 surely is it high time for us to come to an under- 

 standing as to what we may and what we will 

 demand. When Prof. Haeckel declares it to be 

 a question for the schoolmaster to determine 

 whether the theory of descent should even now 

 be made the groundwork of education, whether 

 the plastidule-soul should be assumed as the basis 

 of all our conceptions of Mind, and whether the 

 phylogeny of man should be traced back to the 

 lowest classes of the organic world, or beyond, 

 up to spontaneous generation, in my opinion ho 

 shirks the difficulty. If the theory of descent is 

 so certain as Prof. Haeckel assumes it to be, we 

 must needs demand for it a place in the schools. 

 It is not to be thought of that so weighty a doc- 

 trine, one so revolutionary, so intimately affecting 

 the consciousness of all, a doctrine that of itself 

 constitutes as it were a new religion, should not 

 be implanted bodily in the system of education. 

 How could we bring ourselves to observe abso- 

 lute silence in the schools, with regard to such a 

 revelation, as I may call it, or to leave it to the 

 option of the schoolmaster, whether or not he 

 shall acquaint his pupils with the greatest and 

 most important advances that have been made in 

 science during this entire century ? That, gentle- 

 men, were an act of resignation of the austerest 

 kind, and in reality it never would be practised. 

 The schoolmaster who accepted the doctrine 

 would teach it unconsciously, and he could not 

 do otherwise. He would have to dissimulate, he 

 would at times have to abdicate his own knowl- 

 edge in the most artificial way, so as not to be- 

 tray his acquaintance with and acceptance of the 

 doctrine of descent, or the fact that he knows 

 precisely how man originated and whence he is 

 come ; and if he does not know whither man goes, 

 at least he would think that he knows precisely 

 how in the course of aeons the progressive series 

 has shaped itself. Therefore, I say that, though 

 we were not actually to demand the admission of 

 the theory of descent into the plan of education, 

 it would introduce itself. 



Nor must we forget, gentlemen, that what 

 here we express, perhaps still with a certain timid 

 reserve, is propagated by those outside with a 

 confidence increased a thousand-fold. For in- 

 stance, I once laid down the proposition — in op- 

 position to the doctrine then reigning of the de- 

 velopment of organic life from inorganic matter — 

 that each cell has its origin in another cell, at 



