432 HERMANN VON HELMHOLTZ 



The vital principle was successively the t^vrov 6p^6v t the 

 inherent heat of Hippocrates, deriving from the sacred fire 

 which Prometheus stole from Zeus, later the Trvefyza, the 

 breath of Galen, the anima inscia, the unconscious soul 

 of G. E. Stahl, or the archaeus of Paracelsus, a kind of 

 helpful kobold. The conscious soul of man, again, and even 

 the Holy Ghost, were defined conceptually as the breath or 

 wind, the pneuma, the imparting of it being an inspiration, an 

 inbreathing. 



' Intangible as might be this concept of immaterial substance, 

 and obscure as were its attributes, it was none the less firmly 

 believed in, and the dispute over the substantiality or insub- 

 stantiality of the human soul is vigorously kept up to the 

 present day. And there is no mistaking the cardinal point 

 of the discussion, the essential attribute of substance, its 

 indestructibility, the immortality of the conscious soul ; and, if 

 the vital principle be distinguished from this, the idea of metem- 

 psychosis. 



1 How far the form given to these ideas among the different 

 nations and sects of the human race, has been arbitrary, fantastic, 

 contradictory, and tasteless, need not here be dwelt on. It 

 has been fully discussed in preceding centuries, nor do I here 

 make any claim to solve the ultimate riddles of psychology 

 and the ruling of the Universe. But some actual knowledge 

 of magnitudes, so far agreeing with the old conception of im- 

 material substances, that they are indestructible, incapable of 

 being added to, active in space, but not necessarily divisible 

 with it, has been obtained in the last century. 



' I am not referring to the so-called imponderables, which 

 played an important part in the earlier physics. For these 

 were represented as material substances, like gases, filling 

 space, only not subject to the force of gravity, though endowed 

 with inertia like the heavy masses. Modern physics assumes 

 another such imponderable substance, the so-called lumini- 

 ferous ether, the medium by which space is filled between the 

 ponderable bodies contained in it, which it also penetrates 

 the presence of which is apparent to us, since its oscillations 

 appear as light to our eyes, and produce heat, or electrical 

 and magnetic tensions in the heavy bodies, on which they 

 impinge. 



