VIRCHOW AND EVOLUTION. 



273 



magnetic field, I here lived amid the most complex operations of mag- 

 netism in its twofold aspect of an attractive and a repellent force. Iron 

 was attracted by a magnet, bismuth was repelled, and the crystals oper- 

 ated on ranged themselves under these two heads. Faraday and Plticker 

 had worked assiduously at the subject, and had invoked the aid of new 

 forces to account for the phenomena. It was soon, however, found that 

 the displacement, in a crystal, of an atom of the iron class by an atom 

 of the bismuth class, without any change of crystalline form, produced 

 a complete reversal of the phenomena. The lines through the crystal 

 which were in the one case di'awn toward the poles of the magnet, were 

 driven in the other case from these poles. By such instances and the 

 reasoning which they suggested, magne-crystallic action was proved to 

 be due, not to the operation of new forces, but to the modification of 

 the old ones by molecular arrangement. Whether diamagnetism, like 

 magnetism, was a polar force, was in those days a subject of the most 

 lively contention. It was finally proved to be so ; and the most com- 

 plicated cases of magne-crystallic action were immediately shown to be 

 simple mechanical consequences of the principle of diamagnetic polarity. 

 These early researches, which occupied in all five years of my life, and 

 during which the molecular architecture of crystals was an incessant 

 subject of mental contemplation, gave a tinge and bias to my subsequent 

 scientific thought, and their influence is easily traced in my subsequent 

 inquiries. For example, during nine long years of labor on the subject 

 of radiation, heat and light were handled throughout by me, not as ends, 

 but as instruments by the aid of which the mind might perchance lay 

 hold upon the ultimate particles of matter. 



Scientific progress depends on two factors which incessantly interact 

 — the strengthening of the mind by exercise and the illumination of 

 phenomena by knowledge. There seems no limit to the insight regard- 

 ing physical processes which this interaction carries in its train. Through 

 such insight we are enabled to enter and explore that subsensible world 

 into which all natural phenomena strike their roots, and from which they 

 derive nutrition. By it we are enabled to place before the mind's eye 

 atoms and atomic motions which lie far beyond the range of the senses, 

 and to apply to them reasoning as stringent as that applied by the 

 mechanician to the motions and collisions of sensible masses. But, once 

 committed to such conceptions, there is the risk of being led irresistibly 

 beyond the bounds of inorganic Nature. Even in these early stages of 

 scientific development I found myself more and more compelled to re- 

 gard not only crystals, but organic structures, the body of man inclusive, 

 as cases of molecular architecture, infinitely more complex, it is true, 

 than those of inorganic Nature, but reducible, in the long-run, to the 

 same mechanical laws. In ancient journals I find recorded ponderings 

 and speculations relating to these subjects, and attempts made, by ref- 

 erence to magnetic and crystalline phenomena, to present some satis- 

 factory image to the mind of the way in which plants and animals are 



VOL. SIT. — 18 



