792 HELMHOLTZ. 



eye become through their use that it is not great exaggeration to say- 

 that one may now have a disordered eye repaired, corrected, and set 

 going with little more uncertainty than attends the performance of the 

 same duty for an ill-conditioned chronometer. Had Helmholtz accom- 

 plished nothing except the invention of these instruments, he would 

 have been entitled to the thanks of all mankind, on account of the 

 comfort they have added to life and the pain and suffering they have 

 prevented. 



If I had devoted all of the time allotted to me to a simple enumera- 

 tion! of the contributions to human knowledge made by Yon Helmholtz 

 during fifty years of marvelous intellectual activity, I must have left 

 my task incomplete ; but I must not close without reference to one or 

 two of these, more purely physical in their character and equally 

 stamped with the genius of their author. 



Perhaps Nature has shown herself most reticent and unyielding when 

 scientific men have questioned her as to the ultimate structure of mat- 

 ter, the full knowledge of which includes a satisfactory explanation of 

 the force of gravity, which is one of its essential properties. Hypoth- 

 eses which have been very useful in their time have been finally rejected 

 because they involved some impossible conception, such as action at a 

 distance, which was for a long time believed possible. The tendency is 

 now and has long been to regard space, or at least that part of it in which 

 we have any particular interest, as a plenum, and to assume a continu- 

 ous, incompressible, frictionless elastic fluid in which and of which all 

 things are. In the development of his exquisite theory of vortex mo- 

 tion, Helmholtz demonstrated the possibility of a portion of such a 

 fluid being differentiated from the rest in virtue of a peculiar motion 

 impressed upon it, and that t hen so differentiated it must forever 

 remain so, a fact which was quickly seized upon by Lord Kelvin as the 

 foundation of a vortex theory of matter, thus sharing with Helmholtz 

 the honor of having approached nearer than all others to the solution 

 of the great mystery. 



From the genesis of an atom to the origin of the universe seems a 

 long step, but it is not too great for the intellect of man. The well- 

 known nebular hypothesis was advanced long before Helmholtz's time, 

 but a better knowledge of thermodynamics had quite upset one of its 

 generally accepted principles, namely, that the original nebulous matter 

 was fiery hot. As long ago as 1854, Helmholtz showed that this was not 

 a necessary assumption, and proved that mutual gravitation between 

 the parts of the sun might have generated the heat to which its pres- 

 ent high temperature is due. The greatest philosophers of the past 

 hundred years have attempted to account for this high temperature 

 and for its maintenance, on which all life on this globe depends. The 

 simple dynamical theory of Helmholtz has survived all others, and is 

 to-day universally accepted. 



But I must cut short this absolutely inadequate account of what the 

 scholar did, that I may say a word or two of what the man was. 



