Oct 1 8, 1877] 



NATURE 



533 



to what extent and in what fulness the senses acquaint us with 

 natural phenomena. With regard to the extent we need only 

 point out the boundaries in order to make them perfectly clear 

 to everybody. In time only the present and in spice only 

 that which belongs to our own circumstances is accessible to 

 us. We cannot directly perceive anything of what happened 

 in the past, and of what will be in the future, and nothing that 

 is too distant in space, or that is of too large or too small 

 dimensions. 



With regard to the completeness of sensual ferceptions there is 

 another boundary which is generally not thought of, and upon 

 which I must enter a litile more in detail. Scientific analysis 

 shows the following : — In the totality of force-endowed matter, 

 which we call world, each particle of matter by all its inherent 

 forces is in relation with all others ; it is influenced by all, 

 and in its turn acts upon all, of course according to distances. 

 A conglomeration of particles of course behaves like a single par- 

 ticle ; the effect which it causes and receives is the total of the 

 effects of all single particles. The crystal, the plant, the animal, 

 man are acted upon by the presence of all ma'eriil particles, of 

 each single one by itself and of each conglomeration of particles, 

 and this with reference to all forces which are inherent in them, 

 and consequently with reference to all movements which they 

 perform. But these effects in the infinite majority of cases are so 

 insignificant that they may be neglected as quite imperceptible. 



The thcordkcil possibility therefore exists that the human 

 organism may obtain bodily perceptions of all phenomena in 

 nature. But how is this matter in rcaliiy .' What impressions 

 are so powerful that they become perceptible to us, and which 

 of them are lost, being too insignificant? Amongst the beings 

 known to us, man and the higher animals have the advantage, 

 that certain parts have developed themselves into organs of sensa- 

 tion, which are extremely sensitive for certain natural pheno- 

 mena. Thfse organs of sensation, in the course of numerous 

 and successive species and of innumerable generations within 

 each single species, have been developed from the smallest 

 beginnings to high degrees of perfection. 



The ingenious idea of Darwin that in organic nature only 

 such arrangements at'.ained full development which were useful 

 to the individual bearer, is so simple, so reasonable, and agrees 

 so well with all experience, that physiologists, who alone are 

 competent to decide here, cgree with him perfectly, and are 

 greatly astonished, that a Columbus shcukl not long ago have 

 placed this physiological egg upon its point. 



The degree of perfection which each orgm of sensation has 

 attained in development therefore corresponds exactly to the 

 requirements, and there is not one in which the human organibin 

 is not far surpassed by some animal species, if to the latter the 

 extraordinary fineness of sorr.e particular sensual perception 

 became a condition of its existence. But according tj this boih 

 the human and animal organisms have only dsvelopei organs 

 of sensUion for such external influences as bear upon their 

 existence in a favourable or unfavourable sense. 



We are endowed, for instance, with great sensitiveness for 

 temperature ; it is necessary for our existence, otherwise we 

 might perish through cold or heat without knowing it. We are 

 very sensitive towards light ; it acquaints us in the best and 

 quickeit manner with all objects which surround us and which 

 may be useful or dangerous to us. On the other hand we are 

 not organised to perceive the electricity which surrounds us. 

 While we perceive the increase or decrease of heat and light, 

 we do not know whether the air in which we breathe contains 

 free electricity or not, whether this electricity is positive or nega- 

 tive. If we touch a telegraph wire we cannot feel whether its 

 particles are electrically at rest or in motion. 



It was of no use that the sense for electricity shouM be de- 

 veloped particularly in man and the higher animals, because it is 

 immaterial for the species whether every year some individuals were 

 killed by lightning or not. If this danger were daily to threaten .all 

 individuals, the sense for electricity which the lowest animals pos- 

 sess in its tirst beginnings in the same degree as they possess those 

 for light and heat, would necessarily have developed itself further. 

 We would then perceive by a special organ of sensation the 

 vicinity of a substance in electric tension and be able to escipe 

 the stroke of lightning. We would perceive small changes in 

 the electric state and weak electric currents in our vicinity, and 

 also be able to peer into the secrets of the telegrapli wire. Tlie 

 want of such an organ might easily have been the cause of our 

 total ignorance of electricity. We can very well imagine the 

 atmosphere of the earth without lightning and ihunder. These 

 great electric discharges have helped us to the knowledge oi 



electricity. If accidentally they hid not happened, if, more- 

 over, some quite accidental experiences which revealed an 

 altra:tive and repulsive force generated by friction had not been 

 made, we very probably would have had no idea of electricity, no 

 idea of that force which doubtless plays the greatest part in 

 organic and inorganic nature, which materially affects chemical 

 affinity, which in all molecular motions in organised beings 

 acts perhaps more decisively than any other force, and of which 

 with regard to still mysterious physiological and chemical 

 phenomena we expect the most important explanations. 



Our senses are indeed only organised fir the requirements 

 of our bodily existence but not to satisfy our intellectual 

 cravings, — to acquaint us with all phenomena of nrture and 

 explain them as well. If at the same time t'ley perform this 

 function it is only incidentally. We therefore cannot rely upon 

 our sensual perceptions acquainting us with n// phenomena of 

 nature. Just as in the case of electric phenomena, which occur 

 in every material particle, we have, as it were, learnt something 

 only accidentally, it is easily possible, indeed very probable, that 

 there are still other natural forces, other forms 'of molecular 

 motion, of which we obtain no sensual impressions, because 

 they never unite to any remarkable outcome, and therefore 

 remain hidden to us. 



Our power of perceiving nature directly by our senses is there- 

 fore veiy confined in two aspects. On the one hand we are 

 probably deficient of the power of sensation for who'e domains 

 of natural life, and on the other, as far as we really have this 

 pov/erit is confined in time and soace to an insignificantly small 

 part of the whole. 



It is true that our natural knowledge is not confined to what 

 we perceive with our senses. By conclusions we may also obtain 

 knowledge of what our senses do not reach. The farthest planet 

 of our solar system, Neptune, was known by calculation with 

 regard to its position, its size and weight, before astronomers 

 had discovered it with the telescope. We know, although we 

 cannot see it with the best microscopes, that water consists of in- 

 finitesimal particles or molecules which are in motion, and if it is 

 sugar-water or salt-water, we know perfectly the proportionate 

 weight and the proportionate number of the water, sugar, and 

 salt particles of which it is composed. 



By conclusions from facts which were recog.iised by the senses, 

 we arrive at facts equally certain v/hich can no longer be per- 

 ceived by the senses. We might therefore, perhaps, indulge in 

 the sanguine hope that starting from the small domain which is 

 opened to us by our senses, little by little the entire domain of 

 nature will be conquered by reason. But this hope can never 

 be fulfilled. As the effect of a natural force decreases with its 

 distance, the possibility of knowledge also decreases as the distance 

 in space and time increases. Of the condition, the composition 

 and the history of a fixed star of the least magnitule, of the organic 

 life upon its dark satellites, of the material and spiritual move- 

 ments in these organisms we shall never know anything. In the 

 same way the possibility decreases of discovering a siill unknown 

 natural force, a still unknown lorm of motion of the smallest 

 material particles, the less this force or motion possesses the 

 peculiaiity of accumulating and causing some collective effect. 

 We may consider ourselves fortunate if ever we obtaia only a 

 notion of such a force. 



The confined capacity of the Ego therefore allows us only an 

 extremely fragmentary knowledge of the universe. 



We now pass from the consideration of the subject to that of 

 the object, i.t., the condition and accessibility of nature. The 

 boundaries, which nature herself opposes to our knowledge, are 

 most evident if we adopt the hypothesis that man, on his side, 

 has the most perfect capacity for natural knowledge. This would 

 be the case if the obstacles of time and space did not exist for 

 him, if he could judge of every phenomenon in the past as vyell 

 as he can of everyone in the present ; if the most distant object 

 did not present more difficulty to him than one in his immediate 

 vicinity, and if he could as easily survey the Ingest systems of 

 fixed stars and the smallest atoms, as he can a body of his own 

 size ; it finally he were provided with senses so peifect that all 

 phenomena of nature, all forces and all forms of motion could be 

 perceived directly by him. 



A human race, provided v/ith these perfections might perhaps 

 be enabled to try the solution of Laplace's problem. Laplace 

 says: "A mind, which for a given moment knew all forces 

 which are active in nature, and the respective positions of the 

 beings of which she consists, if it were comprehensive enough to 

 analyse these data —would unite in the same formula the motion 

 of the largest heavenly body and of the lightest atom. Nothing 



