348 HERMANN VON HELMHOLTZ 



you describe would require an extraordinarily exact control, 

 to show that the dependent plate remained symmetrical to the 

 electrical sphere/ 



With the winter of 1883-4 Helmholtz entered on a period of 

 great mathematical exertion in attempting to discover a unifying 

 principle governing Nature, which occupied his thoughts during 

 the last decade of his life, and down to his closing hours. 



His work in thermodynamics had led him to general re- 

 searches upon monocyclic systems, and the deeper significance 

 of the principle of least action ; but the difficulties of working 

 out his ideas had soon accumulated, and his time was much 

 taken up by various official duties. Nor was it only his 

 experimental and mathematical lectures, the management of 

 the Physical Institute, and the lectures at the Military Medical 

 Academy that hindered him from immersing himself in his 

 own ideas. Technical Reports of the most varied character had 

 to be sent in, since his opinion was claimed on all sides as that 

 of the most competent authority. In different places we find 

 reports on the position of lightning conductors for the protection 

 of powder magazines surrounded with earth, on the results of 

 ballooning, and an infinity of other things ; besides, there were 

 musical interests, and all kinds of artistic interests from which 

 he could not and would not separate himself, yet despite all 

 this the profound and fruitful ideas which we shall endeavour to 

 trace in subsequent pages were developing in rapid succession. 



On January 7, 1884, he writes to W. Thomson : 



' I myself am still engaged upon the subject of monocyclic 

 movements, and have now discovered some far-reaching 

 generalizations, which are connected with a universalized form 

 of Hamilton's Law of Mechanics. You had better wait for the 

 later paper before you go on with the monocyclic system ; you 

 will get it in a more convenient form/ 



Even before the Easter holidays he was able to lay a portion 

 of the results of his researches before the Berlin Academy, 

 but was obliged on account of his health to break off his work, 

 and go to England with his daughter Ellen, directly the session 

 was over. 



After seeing Tyndall, Herbert Spencer, Sir John Lubbock, 

 Huxley, and Hooker, the Director of Kew Gardens, he spent 

 some very stimulating days with Sir Henry Roscoe in 



