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a great geologist. I met Mitscherlich, whose researches 

 in crystallographic chemistry and physics had rendered 

 his name illustrious. With Ehrenberg I had various 

 conversations on microscopic organisms. I wanted at 

 the time some amorphous carbonate of lime, and thought 

 that Ehrenberg's microscopic chalk shells might serve 

 my purpose ; but I was thrown back by learning that 

 the shells, small as they were, were built of crystals 

 smaller still. I made the acquaintance of Kiess, the 

 foremost exponent of friction al electricity, who more 

 than once opposed to Faraday's radicalism his own 

 conservatism as regards electric theory. Du Bois- 

 Reymond was there at the time, full of power, both 

 physical and mental. His fame had been everywhere 

 noised abroad in connection with his researches on 

 animal electricity. Du Bois-Reymond is now Perpetual 

 Secretary to the Academy of Sciences in Berlin, and 

 his discourses before that learned body show that his 

 literary power takes rank with his power as an investi- 

 gator. At the same time I met Clausius, known all 

 over the world through his researches on the mechanical 

 theory of heat, and whose first great paper on the sub- 

 ject I translated before quitting Marburg. Wiedemann 

 was there, whose own researches have given him an 

 enduring place in science ; and who has applied his 

 vast powers of reading and of organisation to throwing 

 into a convenient form the labours of all men and 

 nations on voltaic electricity. PoggendorfT, a very able 

 experimenter, was also there. He is chiefly known in 

 connection with the famous journal which so long bore 

 his name. From all these eminent men I received 

 every mark of kindness, and formed with some of them 

 enduring friendships. Helmholtz was at this time in 

 Konigsberg. He had written his renowned essay on 

 the Conservation of Energy, which I translated, and he 



