PROFESSOR IN BERLIN 367 



undue exertions which he had undertaken in Heidelberg. On 

 August 22, his wife, who had hastened to him, writes to Robert : 

 * I found your father weak and ill, and very depressed. He is 

 convinced that he is on the point of death, and is altogether in 

 a curious state. The doctor found himself superfluous in the 

 face of your father's theories and his very limited obedience, 

 and seems to give in to him.' 



In the early days of September he was able to move from 

 Interlaken to Rigi-Kaltbad, and from there went with his wife 

 to visit the Minghettis and Blaserna at Selisberg. 



The painful attacks and mental depression, however, soon 

 reasserted themselves. ' Your father must return home,' writes 

 his wife. ' He wants proper watching and treatment, must have 

 special nourishment, and have done with this hotel life. If we 

 cannot give him mountain air at home we can at least see that 

 he has rest and care, which is something to the good/ 



First, however, they went to consult Kussmaul at Strasburg. 

 ' He listened with great attention, asked clear and precise 

 questions, and then said to me : "I am really unable to find 

 anything amiss, but I would not therefore treat his condition 

 lightly; we can't find out everything by auscultation. Positively 

 ill he is not, but neither is he well. You must take the utmost 

 care as to his diet." ' 



After a rest of some weeks in Baden he recovered almost 

 entirely. 



During his stay on the Rigi, Helmholtz made a series of 

 observations which were the starting-point of his subsequent 

 and fundamental work in meteorology. On October 22, 1886, 

 he sent a brief report to the Physical Society, ' On Clouds 

 and Storm Formation/ describing a phenomenon he had wit- 

 nessed there. One September morning the view of the Jura 

 from the Kanzli on the Rigi was clear, while at a somewhat 

 lower level a layer of light clouds indicated the upper edge of 

 a horizontal layer of dull and heavy air, travelling from North 

 to South, which formed the primary cyclone, by the disturbance 

 and rolling up of its edges. In the course of the day the clouds 

 increased, till by the evening they had formed great masses, in 

 which the separate currents rising from the lower layer could 

 be distinguished, and which were ultimately equalized by the 

 electrical discharges. 



