240 ADDEESS DELIVEKED AT 



that I first heard an honouring and appreciative refer- 

 ence to der Englische Bierbrauer, Joule. 



Stegmann, the professor of mathematics, was also a 

 man of strong individuality. He lectured in a small 

 room on the flat which he occupied. This was the 

 usual arrangement ; each professor had a lecture-room 

 on his own floor, and the students in passing from lec- 

 ture to lecture had sometimes to go from one end of 

 Marburg to the other. The desks were of the most 

 primitive description, and into them the inkhorns were 

 securely fixed by means of spikes at the bottom. Be- 

 sides attending his lectures I had private lessons from 

 Professor Stegmann. He was what I have already de- 

 scribed him to be, an excellent teacher. He lectured 

 on analysis, on analytical geometry of two and three 

 dimensions, on the differential and integral calculus, 

 on the calculus of variations, and on theoretical 

 mechanics. In mathematics he appeared to be entirely 

 at home. I have sometimes seen him, after he had 

 almost wholly covered his blackboard with equations, 

 suddenly discover that he had somewhere made a mis- 

 take. When this occurred he would look perplexed, 

 shuffle his chalk vaguely over the board, move his 

 tongue to and fro between his lips, until he had hit 

 upon the error. His face would then flush, and he 

 would dash forward with redoubled speed and energy, 

 clearing up every difficulty before the end of the lec- 

 ture. It was he who gave me the subject of my disser- 

 tation when I took my degree. Its title in English 

 was ' On a Screw Surface with Inclined Generatrix, and 

 on the Conditions of Equilibrium on such Surfaces.' 

 One evening, after he had given me this subject, I met 

 him at a party and asked him a question, which I did 

 not dream of as touching the solution of the problem. 

 But he smiled and said, 'Yes, Herr Tyndall, but if 



