PROFESSOR AT HEIDELBERG 209 



into one's thoughts and at first one does not appreciate its 

 significance; it is only sometimes that another fortuitous 

 circumstance helps one to recognize when, and under what 

 conditions, it occurred to one ; otherwise it is there, one knows 

 not whence. In other cases it comes quite suddenly, without 

 effort, like a flash of thought. So far as my experience goes it 

 never comes to a wearied brain, or at the writing-table. I must 

 first have turned my problem over and over in all directions, 

 till I can see its twists and windings in my mind's eye, and run 

 through it freely, without writing it down ; and it is never possible 

 to get to this point without a long period of preliminary work. 

 And then, when the consequent fatigue has been recovered 

 from, there must be an hour of perfect bodily recuperation and 

 peaceful comfort, before the kindly inspiration rewards one. 

 Often it comes in the morning on waking up, according to the 

 lines I have quoted from Goethe (as Gauss also noticed, 

 Works, v. p. 609 : Law of Induction discovered January 23, 

 1835, at 7 a.m. before rising). It came most readily, as I ex- 

 perienced at Heidelberg, when I went out to climb the wooded 

 hills in sunny weather. The least trace of alcohol, however, 

 sufficed to banish it. Such moments of fertile thought were 

 truly gratifying, but the obverse was less pleasant when the 

 inspiration would not come. Then I might worry at my 

 problem for weeks and months, till I felt like the creature on 

 the barren heath 



Von einem bSsen Geist im Kreis herumgefuhrt, 

 Und ringsumher ist schSne grune Weide. 



Sometimes nothing but a severe attack of headache could 

 release me from my spell, and set me free again for other 

 interests.' 



To all these great scientific labours and projects were now 

 added no less arduous official duties but in Heidelberg his 

 lectures on physiology and on the general results of science, 

 as well as the direction of the work in the Laboratory, were no 

 mere tasks to be reluctantly fulfilled. Nor did he regard the 

 University lectures simply as an obligation laid upon him by 

 the State, ' which provided him with sustenance, with scientific 

 instruments, and with a good proportion of spare time,' and 

 therewith had the right to claim from him that whatever he 



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