I^JOV. 22, 1877] 



NATURE 



73 



security that it will always remain so for one who, like myself, 

 has had many years' experience of public life. Therefore I think 

 that our efforts should not only tend to claim the attention of all 

 for the moment, but I believe we ought also to ask ourselves 

 what we are to do to maintain the present state of things. I will 

 tell you at once, gentlemen, what I would represent to you as 

 the chief result of my observations, what I would like to prove 

 here principally. I would like to show that for the present we 

 have nothing more to ask, but that on the contrary we have 

 arrived at the point when we must make it our special task to 

 render it possible, through our moderation, through a certain 

 resignation with regard to personal opinions and prtdileclions that 

 the favourable disposition of the nation towards us, which we now 

 enjoy, does not change to the contrary ! 



In my opinion we are really in danger of doing harm to the 

 future, by making use too amply of the liberty which the present 

 slate of things offers us, and I would warn you not to continue 

 in the arbitrariness of personal speculation, which now claims 

 prominence in many domains of natural science. The explana- 

 tions which my predecessors have given you, those of Prof. 

 Nageli in particular, will yield a series of the most important 

 points of view, with regard to the course and limits of natural 

 knowledge, to all who read them, and it cannot be my task to 

 repeat them. But I must point out in reference to them, and I 

 would like to adduce a few practical instances from the experience 

 of natural science, how great a difference there is between what 

 we give out as real science in the stiictest sense of the word, and 

 for which alone we may in my opinion claim the totality of all 

 those liberties which we may designate as liberty of science, or, 

 if we express ourstlves still more exactly, as liberty of sciejttifi: 

 teaching, — and that larger domain, which belongs more to specu- 

 lative expansion, which sets problems, and finds the tasks to 

 which modem investigation is to be applied, and which antici- 

 patively formulates a series of doctrines, which are still to be 

 proved, and the truth of which must yet be found, but which in 

 the mean time may be taught with a certain amount of proba- 

 bility, in order to fill certain gaps in knowledge. We must not 

 forget that there is a limit between the speculative domain of 

 natural science and that which is actually proved and perfectly 

 determined. The demand is addressed to us that this limit shall 

 be not only occasionally pointed out, but fixed with the greatest 

 exactness, so that each single worker shall at all times be per- 

 fectly conscious of where the limit is drawn, and how far he may 

 be requested to admit that what is taught is actual truth. That, 

 gentlemen, is the problem which we have to work out in 

 ourselves. 



The practical questions which are connected with this, lie 

 very near. It is evident that for whatever we consider to be 

 secured scientific truth, we must demand the complete admission, 

 into the scientific treasure of the nation. This the nation must 

 admit as part of itself— xX. must consume and digest it, and 

 continue to work at it. Just in this lies the double promotion 

 which natural science offers to the nation : — On the one hand the 

 material progress, that enormous progress which has been made 

 in modern times. Everything which the steam engine, tele- 

 graphy, photography, chemical discoveries, the research into 

 colours, &c., have produced, all this is essentially based on this 

 — that we, the men of science, complete the doctrines entirely, 

 and when they are perfectly complete and secure, so that we 

 know with certainty that they are natural scientific truths, 

 that we then give them to the nation at large ; then others can 

 work with them as well, and can create new things, of which 

 formerly nobody had any idea, of which nobody dreamt, which 

 come into the world as perfect novelties, and which reform the 

 condition of society and of states. This is the material signifi- 

 cance of our labours. The mental importance, on the other hand, 

 is similar. If I present the nation with a certain scientific truth 

 which is completely proved, to which not the least doubt 

 attaches, if I demand that everybody shall convince himself of 

 the correctness of this truth, that he shall assimilate it, that it 

 shall become part of his thought, then I suppose as a matter of 

 course, that his conception of things generally must be affected 

 by it. Each essentially new truth of this kind must necessarily 

 influence the whole method of conception of man, the method of 

 thinking. 



If, for instance, to refer to a case in point which lies near, 

 we consider the progress which has been made during recent 

 years with regard to the knowledge of the human eye, beginning 

 at the time when the single component parts of the eye were 

 first anatomically separated, when these single and anatomically 

 separated parts were first examined microscopically and their 



different arrangement shown, down to the time when we 

 gradually learned to know the vital qualities and the physio- 

 logical functions of the different parts, until at last, by the 

 discovery of the retina-purple (Sehpurpur) and of its photographic 

 properties, a progress was made of which but a year ago we 

 hardly had an idea, then it is evident that with each progressive 

 step of this kind a certain part of optics, particularly the doctrine 

 of vision, is determined and changed. By this we learn in a 

 perfectly certain manner how the action of light takes place in 

 the interior of the human body itself, and that it is quite an 

 outside organ of the human body, not the brain, but the eye 

 which experiences this action. We learn by it that this photo- 

 graphic process is not indeed a mental operation, but a chemi- 

 cal phenomenon, which occurs by the help of certain vital 

 processes, and that in reality we do not see the external things, 

 but their images in our eye. We are thus enabled to gain a new 

 analytical fact for the knowledge of our relations to the world 

 outside of us, and to separate more distinctly the purely mental 

 part of vision from the purely material part. Thus a certain 

 part of optics, and through it one of psychology, is entirely 

 reformed. Chemistry now steps in to investigate questions 

 which up to the present were entirely out of its range, particu- 

 larly the highly important questions. What is retina-purple ? 

 What substance is this ? How is it formed, how decomposed, 

 and how again formed? The solution of these questions will 

 not fail to open an entirely new field for investigation ; let us 

 hope that also on the field of technical photography we shall 

 soon make some progresr., that we shall learn how to produce 

 many-coloured photographs. Thus a mixture of steps of pro- 

 gress is formed, which belong' partly to the material and partly 

 to the mental domain. And I therefore say, that with each 

 true step of progress in natural knowledge a series of changes 

 must necessarily take place in the internal relations of the human 

 race as well as in the external ones, and nobody can prevent new 

 knowledge from influencing him in a certain sense. Each new 

 part of real knowledge works on in man, it produces new con- 

 ceptions, new trains of thought, and nobody can avoid, after 

 all, placing even the highest problems of the mind into a certain 

 relation with natural phenomena. 



But there is still another side of practical consideration which 

 lies far nearer to us. Everywhere in the entire German Father- 

 land we are now occupied in remodelling educational affairs, in 

 enlarging and developing them, and in determining their precise 

 forms. The new Prussian educational law is on the threshhold 

 of coming events. In all German states larger school-houses are 

 being erected, new institutions are founded, the universities are 

 enlarged, high schools and middle schools are estabhshed. At 

 last the question arises. What is to be the principal tenor of 

 what is taught ? Where shall the school lead to ? In what 

 directions shall it work ? If natural science demands, if we 

 have been exerting ourselves for years to obtain an influence in 

 our schools, if we demand that natural knowledge shall be ad- 

 mitted into education in a much larger measure, so that this 

 fertile material be offered early to the youthful minds, in order 

 to form the basis of a new conception, then we must indeed own 

 that It is high time that we understood one another with regard 

 to what we can and will demand. If Prof. Haeckel says that 

 it is a question for pedagogues whether the theory of descent 

 is now to form the basis of instruction, whether the plasti- 

 dule soul is to be adopted as the basis of all considerations 

 regarding mental phenomena, and whether the phylogeny of 

 man is to be followed up into the lowest classes of the organic 

 empire, and even beyond it up to spontaneous generation, then 

 this is, in my opinion, a mere shifting of tasks. If the theory of 

 descent is as certain as Prof. Haeckel thmks it is, then we must 

 demand its admission into the school, and this demand is a 

 necessary one. How could we imagine that a doctrine of 

 such importance, which influences the conscience of everybody 

 in so revolutionary a manner, which creates directly a soit 

 of new religion, should not be entirely incorporated into the 

 educational plan ! How would it be possible to ignore such a 

 revelation — as I may indeed call it — in our schools, and to kill it 

 by silence as it were, or to leave the transmission of the greatest 

 and most important steps of progress, which our conceptions have 

 made in the whole century, to the option of the pedagogue? 

 Indeed, gentlemen, that would be a resignation of the most 

 severe kind, and in reality it would never be exercised. Every 

 schoolmaster who might receive this doctrine in his mind would 

 teach it as well, even unconsciously. How could he do otherwise? 

 He would have to simulate altogether, he would have to rob 

 himself at times of his own knowledge in the most artificial 



