xxviii 



occupied his vacations in making mineralogical and technological excur- 

 sions. He had resolved to qualify himself as a teacher of Technology, but 

 was unwilling to undertake any definite duties without first seeking to 

 complete his education by studying in other Universities. Accordingly 

 in 1828 he went to Stockholm, where he worked under Berzelius, and had 

 the good fortune to lay the foundation of a warm and life-long friendship 

 with his master; and he visited Paris in 1829 and attended the lectures 

 of Gay-Lussac, Thenard, and other eminent chemists and physicists. In 

 1831 he obtained his habilitation as a teacher of Technology and Physics 

 in the University of Berlin, and laboured as a teacher with unexampled 

 success for nearly forty years. He devoted the utmost care to the arrange- 

 ment of his lectures, and spared neither trouble nor expense in procuring 

 diagrams, models, instruments, and other requisites for their illustration. 

 In 1834 he became Extraordinary Professor in the University. In the 

 same year he passed several weeks in Paris for the purpose of inspecting 

 various manufactories, especially those of chemical products. In the fol- 

 lowing year he came to England and visited various manufacturing esta- 

 blishments in Worcester, Birmingham, Manchester, and Liverpool. On 

 the 27th of January, 1840, he was elected a Member of the Berlin Aca- 

 demy. In the earlier part of his career he lectured on Chemistry at the 

 Gewerbeschule during the absence of Professor Wohler ; from 1832 to 

 1840 he lectured on Physics at the Artillery and Engineer xlcademy ; and 

 from 1850 to 1856 on Chemical Technology at the Gewerbeinstitut. In 

 1845 he became Ordinary Professor. In 1861 he was elected " Rector 

 magnificus" of the University. His services to the Academy were not 

 limited to the publication of original researches in the ' Monatsberichte ' 

 and 'Abhandlungen ;' he devoted much time and labour to its financial 

 affairs. He gave the first impulse to the establishment of the Humboldt 

 foundation for aiding scientific travellers. He was a Member of the Sec- 

 tion of Physics and Chemistry of the Prussian Society of Arts, and one of 

 the twelve Naturforschende Freuude, and for many years took his share in 

 the scientific labours of that Society. He was a Member of the Jury in 

 the London and Paris Exhibitions of 1851, 1855, 1862, 1867. In 1865 

 he represented Prussia in the Conference on weights and measures, which 

 held its session in Frankfort. The deliberations of this Conference finally 

 led to the adoption of the Metric System throughout Germany. 



In the autumn of 1869 he visited England, attended the Meeting of the 

 British Association at Exeter, and then passed some weeks in the Isle of 

 "Wight ; but travelling and change of air no longer produced their accus- 

 tomed restorative effects. After returning to Berlin his labours were olten 

 interrupted by serious indisposition. For months his vigorous constitution 

 struggled against the encroaching sickness. With a sense of duty that 

 overcame the most violent pain, he continued to lecture on Physics, though 

 with many interruptions. On the 25th of February he lectured for the 

 last time. During the month of March he was seldom able to leave his 



