598 MARQUIS DE SAPORTA. 



Theory of Perception of Geometrical Truth, the Doctrine of Energy, 

 Hydrodynamics, and Electrodynamics. Towards the end of his stay in 

 Heidelberg, his attention was more and more turned in the direction 

 of physics and away from physiology. He had certainly become the 

 greatest living German physicist, and when Magnus died, in 1871, it 

 was on all sides agreed that he should be called to take the Director- 

 ship of the Physical Laboratory of the University at Berlin, and 

 natural that he should accept the position. From this time on by far 

 the larger part of his own experimental work was in the domain of 

 jjhysics, though he suggested and helped on to success the researches 

 in physiology of other experimenters, and when it became necessary 

 to review the whole literature of physiological optics on the occasion 

 of the preparation of a new edition of his Handbuch, he spent much 

 time and energy in studying and in drawing conclusions from the work 

 of others in this field. 



Some of the most important of the later contributions of Helm- 

 holtz to mathematical and experimental physics are contained in his 

 papers on, — 



1. Possible Discontinuities in the Motion of a Frictionless Fluid. 



2. The Theory of the Motion of Viscous Fluids. 



3. The Thermodynamics of Chemical Processes. 



4. The Theoretical and Practical Limits to the Resolving Powers of 



Microscopes. 



5. Electrolytical Processes. 



6. The Fundamental Laws of Electrodynamics. 



7. Electrical Oscillations and the Nature of Electricity. 



In 1888 Helmholtz resigned his place at the head of the Berlin 

 Laboratory in order to take charge of the newly established Reiclis- 

 Anstalt at Charlottenburg, and the last years of his life were chiefly 

 spent in organizing the work of this institution. 



GASTON, MARQUIS DE SAPORTA. 



The Marquis de Saporta was born on July 28th, 1823, and died 

 at the age of seventy-one years on January 26th of the present year, 

 at his residence in Aix-en-Provence. 



Since the appearance of his first paper on the Fossil Plants of 

 Provence in 1860, he has been a prominent palaeobotanist, and yields 

 to few cultivators of that science in the number, variety, and impor- 

 tance of his memoirs and larger works. His greatest and most impor- 

 tant work is that on the Mesozoic Flora of France, to which he added 



