i 7 6 THE POPULAR SCIENCE MONTHLY. 



abhors a fallacy or a fiction more than a vacuum ; and though for a 

 stated period the true cause of a given phenomenon may be hidden 

 from view, owing to the imperfect means or the imperfect intelligence 

 employed to unravel it, and thus a fictitious origin be assigned for it, 

 yet in course of time the error is sure to be detected and the truth to 

 be revealed. Thus it was with the astronomical system of Ptolemy. 

 Up to the time of Copernicus the learned world as well as the illiter- 

 ate were led to believe that the sun and all the rest of the heavenly 

 bodies revolved around the earth, as the center of the entire system. 

 Yet, as soon as the error was exploded, and the truth demonstrated, 

 there was a universal rejection of the one and a universal recognition 

 of the other. So, at a later period, when the true theory of ethereal 

 undulations, as applied to light, fought its way against much opposi- 

 tion into popular belief, the old theory of emanations was dropped, 

 never to be again taken up. 



Nevertheless, from what has been said, it must not be inferred that 

 what are called coincidences of thought never occur among scientists. 

 On the contrary, these are so common as to give license for believing 

 in the existence of a law, akin to that of evolution if not a part of it, 

 by virtue of which, in the progress of knowledge, certain new truths 

 dawn upon the world, receiving expression simultaneously from more 

 than one mind. Given the age which is ripe for any discovery, and 

 it breaks out in many different quarters of the globe at the same mo- 

 ment. Men seem to be watching for it, and, like a meteor glancing 

 across the heavens, it is witnessed by several observers from many 

 points of the compass. Take, for example, the great law of natural 

 selection, as applicable to man's origin it was discovered simultane- 

 ously in England by Darwin and Wallace ; while in Germany, at the 

 same time, Haeckel had promulgated a similar theory ; and in France, 

 in a preceding age, Lamarck had laid the foundation for it in the most 

 unmistakable manner. 



But it is only in this single point of occasional coincidence or iden- 

 tity that the leading thoughts of science take on a certain likeness 

 with those of literature. The analogy ends with the admission that 

 each of these thoughts may have rival paternities. Beyond this the 

 difference becomes manifest ; and it consists in this : While the utter- 

 ances of different literatures may seem to be original, this is often 

 owing to a variation in their phraseology, an examination of which 

 will show them to be identical ; and, in addition to this, there is no 

 criterion by which their truth can be tested. But in science, while 

 different claims may be made for originality of discovery, each truth 

 stands out in bold relief, is distinct and well defined, and, after it has 

 been submitted to all the various verifications of which it is suscep- 

 tible, it no longer admits of any doubt and becomes a part of the com- 

 mon stock of human knowledge, possessing, as nearly as possible, the 

 attributes of positive, absolute, and immutable truth. 



