-]-](> THE POPULAR SCIENCE MONTHLY, 



For, on questions such as these, minds of all kinds may be well em- 

 ployed. Here there will be occasion even for those which are not un- 

 conditionally praiseworthy, such as those that habitually doubt, and 

 those to whom the invention of arguments is more pleasing than the 

 mere search for truth. Nay, we may be able to observe the utility 

 even of error. We may not, indeed, wish for a prevalence of errors ; 

 they are not more desirable than are the crime and misery which evoke 

 charity. And yet in a congress we may palliate them, for we may see 

 how, as we may often read in history, errors, like doubts and contrary 

 pleadings, serve to bring out the truth, to make it express itself in 

 clearest terms and show its whole strength and value. Adversity is an 

 excellent school for truth as well as for virtue. 



But that which I would chiefly note, in relation to the great variety 

 of minds which are here, is that it is characteristic of that mental 

 pliancy and readiness for variation w^hich is essential to all scientific 

 progress, and which a great international congress may illustrate and 

 promote. In all the subjects for discussion we look for the attainment 

 of some novelty and change in knowledge or belief ; and after every 

 such change there must ensue a change in some of the conditions of 

 thinking and of working. Now, for all these changes minds need to 

 be pliant and quick to adjust themselves. For all progressive science 

 there must be minds that are young, w^hatever may be their age. 



Just as the discovery of auscultation brought to us the necessity 

 for a refined cultivation of the sense of hearing, which was before of 

 only the same use in medicine as in the common business of life ; or, 

 as the employment of the numerical method in estimating the value of 

 facts required that minds should be able to record and think in ways 

 previously unused ; or, as the acceptance of the doctrine of evolution 

 has changed the course of thinking in whole departments of science 

 so is it, in less measure, in every less advance of knowledge. All such 

 advances change the circumstances of the mental life, and minds that 

 can not or w^ill not adjust themselves become less useful, or must at 

 least modify their manner of utility. They may continue to be the 

 best defenders of what is true ; they may strengthen and expand the 

 truth, and may apply it in practice with all the advantages of expe- 

 rience ; they may thus secure the possessions of science and use them 

 w^ell ; but they will not increase them. 



It is with minds as with living bodies. One of their chief powers 

 is in their self -adjustment to the varying conditions in which they have 

 to live. Generally those species are the strongest and most abiding 

 that can thrive in the widest range of climate and of food. And of all 

 the races of men they are the mightiest and most noble who are, or by 

 self-adjustment can become, most fit for all the new conditions of ex- 

 istence in which by various changes they may be placed. These are 

 they w^ho prosper in great changes of their social state ; who, in suc- 

 cessive generations, grow stronger by the production of a j^opulation 



