SOLUTION OF THE WORLD-PROBLEMS. 385 



century would find themselves in a new world, could 

 they return. But more valuable and important still 

 is the great theoretical expansion of our knowledge of 

 nature, which we owe to the establishment of the law 

 of substance. Once Lavoisier (1789) had established 

 the law of the persistence of matter, and Dalton (1808) 

 had founded his new atomic theory with its assistance, 

 a way was open to modern chemistry along which it 

 has advanced with a rapidity and success beyond all 

 anticipation. The same must be said of physics in 

 respect of the law of the conservation of energy. Its 

 discovery by Robert Mayer (1842) and Hermann 

 Helmholtz (1847) inaugurated for this science also a 

 new epoch of the most fruitful development; for it 

 put physics in a position to grasp the universal unity 

 of the forces of nature and the eternal play of natural 

 processes, in which one force may be converted into 

 another at any moment. 



IV. — PROGRESS OF BIOLOGY. 



The great discoveries which astronomy and geology 

 have made during the nineteenth century, and which 

 are of extreme importance to our whole system, are, 

 nevertheless, far surpassed by those of biology. 

 Indeed, we may say that the greater part of the many 

 branches which this comprehensive science of organic 

 life has recently produced have seen the light in the 

 course of the present century. As we saw in the 

 first section, during the century all branches of 

 anatomy and physiology, botany and zoology, ontogeny 

 and phylogeny, have been so marvellously enriched 

 by countless discoveries that the present condition of 

 biological science is immeasurably superior to its 



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