Oct. 25, 1877] 



NATURE 



56: 



in nature. Mental force is the capacity of material particles to 

 act upon each other. The mental phenomenon is the perform- 

 ance of this action, which consists in motion, therefore in a 

 change of position, of the material particles and the forces 

 inherent in them, and by this leads directly to a new mental 

 occurrence. Thus the same mental chain encircles all material 

 phenomena. 



The human mind is nothing else but the highest development 

 upon our earth of the mental phenomena which move and ani- 

 mate nature everywhere. But it is not the product of secretion 

 of the cerebral substance ; as such it would be withor.t further 

 influence upon the brain, just as the secreted gall is of no further 

 signification for the liver. On the contrary, sensation and con- 

 sciousness have their firm seat in the brain, with which they are 

 iiidissolubly united, and in which, by their intervention, new 

 conceptions are formed and converted into actions. Just as the 

 stone would not fall down if it did not feel the presence of the 

 earth, so the trampled worm would not wriggle if it had no 

 sensation, and the brain would not act reasonably if it had no 

 consciousness. 



This conception satisfies our causal demands entirely. For 

 the naturalist it is a logical necessity to admit only differences of 

 degree in finite nature. In the same way as there is a common 

 measure for everything in space as well as for everything in time, 

 so there must be a common measure for all mental phenomena. 

 In the same way as there are gradations in material nature from 

 the most simple to the most complex, so there must be similar 

 gradations in mental nature, which isj parallel to the former. It 

 is true that in atoms and molecules we do not yet find pleasure 

 and pain or love and hate pronounced with decision, but yet we 

 find the first germs, as it were the original beginnings, of these 

 feelings, and it would be the task of a comparative psychology 

 to follow consciousness through unconscious sensation down to 

 the insensible action of material particles. 



But the domain of the mind offers far greater difficulties to 

 our investigation than the material domain, because we can only 

 use our subjective perceptions as immediate experience, and 

 because we do not possess a special organ of sense which enables 

 us to make objective observations of other bodies. The obser- 

 vation with our senses, which are organised for quite different 

 objects, acquaints us only in a roundabout way and in a very 

 defective manner with the mental occurrences in other beings, 

 and our judgment of them is all the more uncertain the further 

 we depart in nature from the human species itself. It will 

 therefore, perhaps, never be possible to find the measure for the 

 mental phenomena really, to determine it, and to raise compara- 

 tive psychology to the rank of a natural science. 



Natural knowledge remains limited to what is finite, the natu- 

 ralist must therefore confine himself strictly to the finite only. 

 The demand, which is often addressed to him, that he should 

 have a more pliilosophical mind, that he should criticise in a 

 philosophical manner, because it is impossible to avoid meta- 

 pliysical speculation entirely, only shows how difficult it is to 

 separate two absolutely different domains, which have once been 

 mixed up only to produce general confusion. The power of 

 education and habit also was, up to the most recent period, an 

 obstacle in the way of a complete and radical separation of these 

 two domains, and yet it is certain, and we know by experience, 

 that every metaphysical addition turns natural science and natural 

 investigation into a turbid and muddy alloy. 



Natural science must be exact ; it must rigidly avoid cveiy- 

 thing which oversteps the limit of the finite and the intelligible, 

 and which is transcendental ; it must proceed in a strictly 

 materialistic manner, because its sole object is finite, force- 

 endowed matter ; and it must not forget that this true materialism 

 is an empirical and not a philosophical one, and that it is 

 bounded by the same limits as those of the domain upon which 

 it moves. 



I do not wish to say by this that the naturalist is not allowed 

 to philosophise, that he is forbidden to move in ideal and 

 transcendental domains. But he ceases to be a naturalist, and 

 the only thing, which from his vocation is perhaps of advantage 

 to him, is that he keeps both domains strictly apait ; that he 

 knows how to treat the one as the pure domain of investigation 

 and knowledge, and the other, while he frees it from everything 

 that is finite, as the hidden domain of presentiment. 



To the human mind, to our desire of investigation and know- 

 ledge, the whole sensually-perceptible world is open. We pene- 

 trate into the greatest distances by means of the telescope and 

 calculation, and into the smallest sjiaces by means of the micro- 

 scope and combination. We investigate the most comple.x and 



complicated organism, which belongs to ourselves, in the most 

 varied directions. We recognise the forces and laws governing 

 nature, and through this we subject the whole inorganic and 

 organic world, as far as we can reach it. If man reviews the 

 triumphs in the domains of science and power which have been 

 obtained up to the present, and thinks of the still greater future 

 conquests, then he may with pride feel himself lord of the world. 



But what is this world, over which the human mind reigns ? 

 Not even a grain of sand in the eternity of space, not even a 

 second in the eternity of time, and only an outwork of the true 

 essence of the universe. Because even of the infinitesimal world, 

 which is accessible to us, we only know what is changeable and 

 perishable. All that is eternal and stable, the houi and the wliy 

 of the universe, remains for ever incomprehensible to the human 

 mind, and if it tries to overstep the limit of finiteness it can 

 only puff itself up to a ridiculously-adorned idol, or desecrate the 

 eternal and the divine by human disfiguration. Even llie 

 matured mind, which would have arrived at complete natural 

 scientific insight, and would wish to free the divine of everything 

 finite and perishable, could, in its restriction, make of divinity 

 only a constitutional phantom-king, who, according to the words 

 of a statesman recently deceased, would "reign, but not govern. ' 

 In the finite world the eternal natural forces rule unalterably, 

 and we recognise their effects in the laws of motion and change. 

 Whether and how they are the tenor and expression of a 

 conscious eternal design is past our comprehension. 



If my predecessor, Prof. Du Bois Reymond, ended his address 

 with the crushing words. Ignoramus, et is;noyal>imus, then I 

 close mine with the conditional but more consolatory utterance 

 that we do not merely know, but really understand the fruits of 

 our investigations, and that our knowledge bears in itself the 

 germ of an almost infinite growth, without, however, approaching 

 omniscience by the smallest step. If we practise reasonable 

 resignation, if, as finite and perishable human beings, as we are, 

 we are satisfied with human insight, instead of claiming divine 

 knowledge, then we may say v^ith full confidence — 

 " We know, and we shall know ! " 



T 



ON THE SOLAR ECLIPSE OF AGATHOCLES 

 B.C. 310 (isth August).' 

 HE mean motion of the moon round the earth was formerly 

 assumed to be constant, until Halley showed that it has 

 been gradually increasing by a small amount during the last few 

 thousand years. Halley made this discovery by the study of 

 ancient solar eclipses, which were found always to occur to the 

 mstiaardoi their calculated places : — this indicates a slower mean 

 motion of the moon in former times, as may be thus shown — a 

 spectator in the northern hemisphere looking at a solar eclipse 

 will face the south, having the west on his right hand, and the 

 east on his left hand ; and he will see the moon cross the sun's 

 disc from right to left. When we calculate backwards to an old 

 eclipse (attributing to the moon her present mean motion), we 

 are, in fact, unwinding, from left to right, the path she has 

 described since the eclipse happened, and by this unwinding 

 process we find that we always pUce the moon to the right [west) 

 of the place where she was actually when the eclipse occurred. 

 Thus, all the ancient eclipses being observed at places to the 

 castivard (hfl) of their calculated places of observation, we learn 

 that the moon's mean motion was formerly slower than it now is. 

 The coefficient of the moon's mean motion, found by Halley, 

 from ancient eclipses, was 



I0'2 X «", 



where n is" the number of centuries. 



The acceleration of the moon's mean motion was first explained 

 by Laplace, who showed that the mean central disturbing force 

 of the sun, by which the moon's gravity towards the earth is 

 diminished, depends not only on the sun's mean distance, but on 

 the eccentricity of the eartli's orbit. This eccentricity has been 

 diminishing for many ages, while the mean distance remains 

 unaltered. In consequence of this, the sun's mean' disturbing 

 force is diminishing, and, consequently, the attraction of the 

 moon towards the earth has been increasing, and with it, of 

 course, the mean motion of the moon has been also increasing. 

 Thecalculations of Laplace, confirmedandextendedbyDamoiseau 



■ Paper read before the Mathematical Section of the British Association, 

 Plymouth, 1877, by Rev. Dr. Samuel Haughton, F.R.S. (Trm. Coll. 

 Dublin.) 



