254 THE SCIENTIFIC WORK OF GEORGE SIMON OHM. 
task, he was called to Munich as curator of the mathematical and 
physical collection of the Royal Academy of Sciences. He was also to 
be adviser of the ministerial director of telegraphs, and was obliged to 
lecture on mathematics and physies as professor at the university: 
Thus for the man of sixty the desire of his youth was tardily fulfilled, too 
tardily and hence scarcely to the benefit of science. The manifold duties 
of his new sphere of activity prevented the completion of his great 
work, and robbed posterity of the legacy which Ohm had intended to 
leave it from the rich treasures of his thoughts. However, it is by no 
means true that this period at Munich was entirely without gain for 
science. Opties had always been a pet object of his activity. In 1840 
in Poggendorff’s Annalen, vol. XLIX, he published a “ Description of some 
simple and easily managed arrangements for making the experiment 
of the interference of light.” Init he showed how French interference 
prisms which worked very well could be made from common plate glass ; 
indeed, how a simple strip from the edge of a piece of plate glass could 
be used for the purpose. In 1852 and 1853 in his great work, “‘ Expla- 
nation of all pereeivable interference phenomena of plates of miaxial 
erystals in plane-polarized light,” heset himself the task of develop- 
ing ina most general way than had been done, the theory of these 
phenomena so rich in form and color. He arrived at a formula of great 
simplicity and beauty, and which covered all the individual colors. 
This work has many points in common with one by Prof. Sangberg 
of Christiania, published complete in Norwegian in 1841, in the ‘‘ Ma- 
gazin for Naturvidenskaberne” (natural sciences), and abstracted in 1842 
in the first extra volume (Hrgdnzungsband) of Poggendorff’s Annalen. 
The title of Sangberg’s work was, ‘‘ Analysis of the isochromatice curves 
and the interference phenomena in combined miaxial crystals.” Ohm 
first learned of this work after the completion of his own, which was, 
however, by no means rendered superfluous by Sangberg’s. The phe- 
nomena of elliptical interference rings which had led Ohm to his inves- 
tigation, had also been observed at the same time by Sangberg. 
Among the causes which prevented Ohm from continuing and com- 
pleting his molecular physics was the writing of a text-book of physics 
for his students. In spite of the “aversion always felt to working out 
a text-book,” he still felt impelled to the work by having accepted the 
position of instructor. He accomplished the speedy completion of this 
thoroughly original work by lithographing his lectures as fast as they 
were delivered and giving copies to his classes. The strain caused by 
so quick an accomplishment of so difficult a task had a bad effect upon 
his health, as he sadly acknowledges at the close of the preface of his 
text-book (Easter, 1854). One other expression in the text of the book 
dimly suggests his feeling that his strength wasexpended. As a result 
of repeated attacks of epilepsy, on July 6, 1854, he yielded up that life 
which to its last breath was devoted to the search after truth. 
