PROFESSOR AT HEIDELBERG 183 



The universal recognition of Helmholtz's acoustic achieve- 

 ments by the scientific world, and his election to the Corre- 

 sponding Membership of the Academy at Vienna, and the 

 Scientific Society at Erlangen, had filled his aged father with 

 pride and delight, and as the old man ' had felt much better of 

 late, and the indications of brain trouble were quite insignificant', 

 it was an unexpected shock to Helmholtz to receive the news 

 on June 4 that his father had had a stroke, and lay at death's 

 door. He started at once for Potsdam, leaving his sick wife 

 with a heavy heart, but his father died before his arrival. ' The 

 circumstances/ he writes to his wife, ' were much the same as 

 in my mother's case, only the stroke was less rapidly fatal.' 



Helmholtz returned from the funeral to find little comfort 

 in his own house ; his wife's health was failing irrevocably, 

 slowly at first, but afterwards very rapidly. 'Nothing did good,' 

 writes her sister, ' and at length we gave up all hope ; Heidel- 

 berg knew only the shadow of her former self.' Helmholtz 

 suffered severely from all this agitation ; his frequent migraines, 

 which were becoming more frequent and serious, obliged him 

 at the doctor's orders to go off to Switzerland at the beginning 

 of the autumn holidays, a change that was always beneficial. 

 But he was shortly recalled to Heidelberg by disquieting news 

 of his wife's health, and came back to sad and heavy months, 

 in which his only comfort lay in the severest intellectual 

 discipline. 



At the outset he went on with the work commenced during 

 the previous summer, on friction in fluids : ' I have just begun 

 some work on friction in fluids with Piotrowski, in which he 

 will do the experimental part. I hope we shall get the funda- 

 mental hydrodynamic equations in reference to friction out of 

 it. After that, any special work on the motion of fluids would 

 be reduced to a mathematical problem, although it would only 

 be resolvable in a very few cases/ 



But this most arduous mathematical work, which required 

 the greatest mental concentration, proved impossible in his 

 perpetual preoccupation and anxiety over his wife's illness, 

 and he turned for distraction to easier experimental questions 

 in optics and acoustics, as an appendix to his earlier work. 



On Nov. n, 1859, he gave a lecture to the Nat. Hist. 

 Med. Verein, on ' Colour-Blindness ', which led on from his 



