MIND AS A MEASURE OF NATURE. 683 



for it. In like manner, we have sufficient reason, judging merely from 

 the observation of previous speculation, to warrant us in abstaining 

 from attempts to deduce a knowledge of material nature from mental 

 concepts. Add to this fact that other, that all knowledge has its 

 basis in experience, and we supplement our empirical conclusion by a 

 deduction from a fundamental law of nature, and show their entire 

 congruence. 



Early physical speculation, with hardly an exception, proceeds on 

 the assumption that knowledge is derived primarily from the mind 

 thus completely inverting the true order. Would some of those per- 

 sons who in our day attribute so much power to the unaided mind 

 carefully peruse a history of science in the early centuries of our era 

 and the centuries immediately preceding it, we think they would be- 

 come convinced that purely mental speculation can never lead to any 

 exact knowledge, but must, on the contrary, invariably be a source of 

 obscurity and error. 



With but two or three exceptions, the most eminent men of the 

 early and middle ages, except as in a few instances they recorded in- 

 teresting facts, contributed absolutely nothing to scientific progress. 

 The principal cause of the difference in the civilization of our times 

 and those of the ancients is the progress of exact knowledge. What 

 would the most mystical of metaphysicians of to-day say to Socrates's 

 assertion that those things are called like which partake of the quality 

 of likeness ? or to Aristotle's argument against a void in nature, that 

 a void is a negation, and in a negation there could be no differences, 

 and where there were no differences there could be no up or down, 

 consequently bodies could not move up or down in a void, but it is 

 the nature of bodies to move up and down, therefore there is no void ? 

 or to his argument in support of circular motion, that it is the best, 

 therefore the most natural ? The mental ability of the " Father of 

 Logic " is unquestioned. He follows logical methods closely enough. 

 What, then, is there unscientific in his reasoning ? Simply that he 

 allows abstract terms and mental notions to pass current for facts 

 thus using an irredeemable currency as though it possessed intrinsic 

 value. 



The modern astronomer can not but wonder at the daring specula- 

 tions of the Pythagoreans, that, as ten was a perfect number, there 

 must be ten heavenly bodies, notwithstanding nine only were then 

 known. Before such vaticinations the predictions of a Leverrier sink 

 into insignificance. 



We find the whole history of science, up to the time of Copernicus, 

 a history of the conflict of facts with preestablished notions. The 

 problem of astronomers was to reconcile the apparent motions of the 

 heavenly bodies with their assumed circular motions. Thus, when it 

 was found that the motions of the planets were not uniformly circu- 

 lar, it was naively suggested that an uncertain motion could not be 



