NA TURE 



[November 26, 1S91 



Returning to the suppositions upon which (7) was 

 founded, we see that> if the bodies be all of one shape, 

 e.g. spherical, the formula contains only two constants — 

 one determining the size of the bodies, and the second 

 the intensity of the cohesive force ; for the mean kinetic 

 energy is supposed to represent the temperature in all 

 cases. From this follows the theorem of Van der Waals 

 respecting the identity of the equation for various 

 substances, provided pressure, temperature, and volume 

 be expressed as fractions of the critical pressure, tem- 

 peraiure, and volume respectively. If, however, the 

 shape of the bodies vary in different cases, no such con- 

 clusion can be drawn, except as a rough approximation 

 applicable to large volumes. Rayleigh. 



Terling Place, Witham, November 18. 



THE IMPLICATIONS OF SCIENCE} 

 II. 



I MIGHT now at once return to further consider those 

 implications of science to which I have called your 

 attention, but I think it will be better to first briefly pass 

 two important matters in review. 



The first concerns our means of investigation as to 

 such fundamental questions. 



The second relates to our ultimate grounds for forming 

 judgments about them. We have to consider how funda- 

 mental truth can be acquired and tested. 



Evidently the only means of which we can make use 

 are our thoughts, our reason, our intellectual activity. 

 " Thoughts " may be, and should be, carefully examined 

 and criticized ; but however much we may do so, and 

 whatever the results we arrive at, such results can only 

 be reached by thoughts, and must be expressed by the 

 aid of our thoughts. This will probably seem such 

 a manifest truism that I shall be thought to have com- 

 mitted an absurdity in enunciating it. To suppose that 

 by any reasoning we can come to understand what we 

 can never think, may seem an utterly incredible folly ; 

 yet at a meeting of a Metaphysical Society, in London, 

 a speaker, not long ago, expressly declared "thought" 

 to be a misleading term, the use of which should be 

 avoided. 



Now I am far from denying that unconscious activities 

 of various different orders take place in our being, yet 

 whatever influence such activities may have they cannot 

 affect our judgments save by and in thoughts. 



If a man is convinced that thoughts are worthless tools, 

 he can only have arrived at that conclusion by using the 

 very tools he declares to be worthless. What, then, ought 

 his conclusion to be worth even in his own eyes ? 



It is simply impossible by reason to get behind or 

 beyond conscious thought, and our thoughts are and must 

 be our only means of investigating problems however 

 fundamental. 



Even in investigating the properties of material bodies, 

 it is to self-conscious reflective thought that our final 

 appeal must be made. 



For it is to our thoughts, and not to our senses only, 

 that our ultimate appeal must be made, even with respect 

 to the most material physical science matters. 



Some persons may imagine that with respect to investi- 

 gations about the properties of material bodies, it is to 

 our sensations alone that we must ultimately appeal. 

 But it is not so ; anyone would be mad to question the 

 extreme importance, the absolute necessity, of our sensa- 

 tions in such a case. Nevertheless, after we have made 

 all the observations and experiments we can, how can we 

 know we have obtained such results as we may have 

 obtained, save by our self-conscious thought } By what 



' Friday Evening Discourse delivered at the Royal Institution by Dr. St. 

 George Mivart, on June 5, 1891. Continued from p. 6;;. 



NO. 1 152, VOL. 45] 



other means are we to judge tetween what may stem 

 to be the conflicting indications of different sense 

 impressions? 



Our senses are truly tests and causes of certainty, butnot 

 the test. Certainty belongs to thought, and self-conscious 

 reflective thought is our ultimate, absolute criterion. 



As to the ultimate grounds on which our judgments re- 

 specting such problems must repose, as Mr. Arthur 

 BaliGUi has forcibly pointed out, that it is a question 

 altogether distinct from that of the origin of our judg- 

 ments, or from reasonings about their truth . Such matters 

 are very interesting, but they are not here in point, since 

 it is plain that no proposition capable of proof can be one 

 the certainty of which is fundamental. For, in order to 

 prove anything by reasoning, we must show that it 

 necessarily follows as a consequence from other truths, 

 which therefore must be deemed more indisputable. But 

 the process must stop somewhere. We cannot prove 

 everything. However long our arguments may be, we 

 must at last come to ultimate statements, which must be 

 taken for granted, like the validity of the process of reason- 

 ing itself, which is one of the implications of science. If 

 we had to prove either the validity of that process or such 

 ultimate statements, then either he must argue in a circle, 

 or our process of proof must go on for ever without com- 

 ing to a conclusion, which means there could be no such 

 thing as " proof" at all. 



Therefore the "grounds of certainty" which any 

 fundamental proposition may possess cannot be anything 

 external to it — which would imply this impossible proof. 

 The only ground of certainty which an ultimate judgment 

 can possess is its own self-evidence — its own manifest 

 certainty in and by itself. All proof, all reasoning, must 

 ultimately rest upon truths which carry with them their 

 own evidence, and do not therefore need proof. 



It is possible that some of my hearers may be startled 

 at the suggestion of believing anything whatever on " its 

 own evidence," fancying it is equivalent to a suggestion 

 that they should believe anything blindly. This, I think, 

 is due to the following fact of mental association. The 

 immensely greater part of our knowledge is gained by us 

 indirectly — by inference or testimony of some kind. 



We commonly ask for some proof with regard to any 

 new and remarkable statement, and no truths are brought 

 more forcibly home to our minds than are those demon- 

 strated by Euclid. Thus it is that many persons have 

 acquired a feeling that to believe anything which cannot 

 be proved, is to believe blindly. Hence arises the 

 tendency to distrust what is above and beyond proof. We 

 are apt to forget, what on reflection is manifest— namely, 

 that if it is not blind credulity to believe what is evident 

 to us by means of something else, it must be still less 

 blind to believe that which is directly evident in and by 

 itself. 



And self-conscious reflective thought tells me clearly, 

 that the law of contradiction is not only implied by all 

 science, and necessary to the validity of all science, but 

 that it is, as I said, an absolute, necessary truth which 

 carries with it its own evidence. It must be a truth, then, 

 applicable both to the deepest abyss of past time and the 

 most distant region of space. But here, again, I think it 

 possible that one Jor two of my hearers may be startled, 

 and perhaps doubting how things in this respect may be 

 in the Dog-star now, or how they were before the origin 

 of the solar system, I fancy I hear someone asking: 

 " How is it possible that we, mere insects, as it were, of a 

 day, inhabiting an obscure corner of the universe, can 

 know that anything is and must be true for all ages and 

 every possible region of space.?" 



In the first place, 1 think the difficulty which may be 

 thus felt is due to the abstract form of the law of con- 

 tradiction. And yet, as I said before, it is but the 

 summing up of all the particular instances, as to each 

 one of which no difficulty at all is felt, but each is clearly 



