130 ALEXANDER VOX HUMBOLDT. 



owner of some salt works in Savoy and of. some sulphuric acid 

 works in Winterthur, and has besides the direction of all the 

 salt works in Bavaria. I plied him with questions from morning 

 till night, and I sc arcely know anyone whose conversation I have 

 found so instructive. He wrote of his own accord to tell me 

 that he considered my treatise the best that has been written 

 upon the manufacture of salt. I now see the subject in a 

 clearer light, and I mean to postpone the publication till the 

 autumn. I have gained a great deal of information from Claiss, 

 and have got possession of some of Franklin's manuscripts upon 

 methods of heating ; I also wish to complete my chart, showing 

 the connection between all the salt springs of Grermany. I don't 

 think I have mentioned to you anything about this map. It ori- 

 ginated from an essay appended to my report from Bayreuth, 

 " On the Method of Boring for Brine." The leading ideas 

 are that the mountains of Franconia, Suabia, and Thuringia 

 have one main position of strata, that they are connected by a 

 valley extending from twenty to thirty miles between Eisenach 

 in the mountains of the Thuringian Forest and Osterode among 

 the isolated Hartz Mountains, that all the brine in Franconia 

 and Suabia flows in the upper gypsum, that all the salt springs 

 in Grermany lie in one given direction, that it is possible to 

 draw lines upon the map, by following which salt springs may 

 be found mile after mile, that these salt streams follow the 

 general slope of the land, which throughout Grermany is from 

 the south-west to the north-east, and flow round the primi- 

 tive rocks wherever these project above the surface.' 



Even in later years Freiesleben frequently expressed regret 

 that this map, showing the course of the salt-streams of Grer- 

 many, and the treatise on the method of boring for brine, had 

 never been printed and were unfortunately lost. 



The last of the few letters still preserved of this journey is 

 dated Buchwald, January 14, 1793: 



' I was three weeks,' writes Humboldt, ' in Breslau, and the 

 rest of the time at Waldenburg and Kupferberg among the 

 Eiesengebirge. Never longer than two days in a place, travel- 

 ling in the midst of extreme cold and far into the night, that I 

 might at least visit the principal mines, I found no possible 

 opportunity of writing to you. At Breslau I stayed three weeks 



