PROFESSOR VIRCHOW AND EVOLUTION. 385 



most complicated cases of magne-crystallic action were 

 immediately shown to be simple mechanical conse- 

 quences of the principle of diamagnetic polarity. These 

 early researches, which occupied in all five years of my 

 life, and throughout which the molecular architecture 

 of crystals was an incessant subject of mental contempla- 

 tion, gave a tinge and bias to my subsequent scientific 

 thought, and their influence is easily traced in my 

 subsequent enquiries. For example, during nine years 

 of labour 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 per- 

 chance lay hold upon the ultimate particles of matter. 

 Scientific progress depends mainly upon 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 

 regarding physical processes which this interaction car- 

 ries 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 mo- 

 tions 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 concep- 

 tions, there is a risk of being irresistibly led beyond 

 the bounds of inorganic nature. Even in those early 

 stages of scientific growth, I found myself more and 

 more compelled to regard not only crystals, but organic 

 structures, the body of man inclusive, as cases of molec- 

 ular 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 



