HELMHOLTZ IN BERLIN 



Electrodynamics and Theories of Electricity ; (4) 

 On Meteorological Physics ; (5) On Optics ; and (6) 

 On the Principles of Dynamics. 



I. On the Conservation of Energy. 



This has already been dealt with in Chapter V., and 

 it has been shown that Helmholtz played an important 

 part in formulating, from a mathematical standpoint, 

 this great principle. 1 In the labours of his after 

 life it was his guiding star. It pointed out the path 

 of research, while it was the final test to which all 

 theories were submitted. The tract not only estab- 

 lished the theory from general principles, but it con- 

 tained illustrations of an electrical character to which 

 reference is still made in all discussions of the subject. 2 

 In later researches he verified Lord Kelvin's doctrine 

 of the dissipation of energy that only certain forms of 

 energy can be completely changed into others a 

 result in accordance with the second law of thermo- 

 dynamics, which asserts that it is impossible, by the 

 unaided action of natural processes, to transform any 

 part of the heat of a body into mechanical work, 

 except by allowing heat to pass from that body into 

 another at a lower temperature.3 This is the modern 



1 See Tait's Sketch of Thermo-dynamics, p. 68. Edinburgh, 1877. 



2 Clerk Maxwell. Electricity and Magnetism, vol. ii., p. 176. Ox- 

 ford, 1873. 



3 Clerk Maxwell. Theory of Heat, p. 153. London, 1872. 



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