42 Obituary Notices of Felloivs deceased. 



succeed Eisenlohr, and in 1871 he entered upon the Professorship of 

 Physical Chemistry in the University of Leipzig. For sixteen years 

 he had been teaching pure physics, but his early chemical studies, 

 which a well-marked chemical side to several of his latter experimental 

 researches had helped to keep alive, enabled him to discharge the 

 duties of this new office without too great difficulty; but when, in 

 1887, on the retirement of his colleague Hankel, he was offered the 

 Professorship of Physics, he was glad to be able once more to concen- 

 trate his activity upon a single branch of science. The duties of this 

 last office he continued to discharge practically up to the time of his 

 death, which occurred on the 21st March, 1898. 



One of Wiedemann's earliest experimental investigations related to 

 the comparative thermal conductivities of the metals ; his results long 

 remained the most trustworthy that existed on the subject, and even 

 now they have scarcely been superseded. Other researches dealt with 

 electrical endosriiose, the electrical resistance of electrolytes, the rela- 

 tion between the magnetic properties of compound bodies and their 

 chemical composition, the influence of mechanical strain on the 

 magnetic properties of the magnetic metals, and many other subjects. 

 His magnetic researches, which were very thorough and long-sustained, 

 brought to light a remarkable parallelism between the laws and 

 effects of torsion and those of magnetisation, and led him to the dis- 

 covery of several phenomena which were rediscovered later by other 

 investigators. 



A determination of the value of the ohm when expressed in terms 

 of the specific resistance of mercury, the final results of which were 

 published in 1891, led Wiedemann to a number which hardly differs 

 to an appreciable extent from what is now admitted as the most exact 

 value and affords a striking- example of his care and accuracy in 

 quantitative experiment. 



But great as were Wiedemann's achievements as an original investi- 

 gator, they were surpassed in importance by his literary labours. 

 The editing of the ' Annalen der Physik und Chemie,' which he under- 

 took in 1877 and continued to the end of his life, would be considered 

 sufficiently laborious by most men who are already actively dis- 

 charging the duties of an important University Professorship ; but in 

 his case it was a comparatively small addition to the work he was 

 already engaged in. The ' Lehre vom Galvanismus und Elektromag- 

 netismus,' or, as it afterwards became, ' Die Lehre von der Elektricitat/ 

 forms the most obvious and visible result of Wiedemann's work. The 

 first edition appeared in 1861, and its revision and extension in three 

 subsequent editions, the last of which was completed little more than a 

 year ago, was a practically continuous occupation for the rest of the 

 author's life. It is a monument of industry, untiring and judicious, 

 and for accuracy and completeness it has no rival in any other branch 



