book_cover_big.gifHermann von Helmholtz is a famous name in thermodynamics[1] although he also made famous inventions in the fields of ophthalmology, electrochemistry and acoustics. It was Helmholtz who formulated very clearly, using conclusions reached by Kelvin, Joule and Clausius earlier,  the existence of the law of conservation of energy or of “force” (as energy was called at that time) around 1850. In the winter of 1862, he delivered a series of lectures at Carlsruhe on the topic of the “Conservation of Force”. He started with an introduction in which he managed to elaborate on this theme without using any mathematical formula[2]. Below I will give a brief summary of the main points of this introduction (which can be found on numerous web sites[3]).

He starts of by showing that gravity, the most fundamental of all forces,  can be used to do work[4]. For instance a weight can drive a clock by sinking. Although the weight will have lost it capability to perform work when it reaches the floor, it will not loose its weight: gravity remains. The amount of work can then be determined by the weight times the distance travelled.

Heat can also produce work such as occurs in a steam engine. Here he recalls the point that heat must not be considered as a substance but merely as an movement of internal particles (realize that we are still about 50 years before atoms become widely accepted!). For quite a while it was considered that the amount of heat was constant (for instance, the required amount of heat required to melt a piece of ice is the same amount that one needs to extract when the resulting water is converted to ice again). However, he explains that as soon as heat is converted into work, that an equivalent amount of heat is destroyed. The relationship between heat and work was established by the work of Clausius and Joule. Many other examples exist where work is generated at the cost of something:

  • a raised weight can do work but while doing that it must sink and no longer do work
  • a stretched spring can do work but will become loose
  • the velocity of a mass can do work but will eventually come to rest
  • chemical forces (=energy) can do work but they will get exhausted
  • electrical force can do work but will consume chemical or mechanical forces

Helmholtz concluded that all natural forces (energy) can do work but they are at the same time exhausted to the degree of work performed. He then formulated that the total quantity of all forces capable of doing work in the whole universe remains constant. He compared this with the laws of constant mass or constant chemical elements (both were of course to be found less constant after the theory of relativity and the discovery of radioactivity!!).

Finally he touches briefly on the topic of perpetual motion and states that force cannot be produced from nothing: something must be consumed. I strongly recommend reading Helmholtz’ introduction.

See also: https://secondlawoflife.wordpress.com/2007/12/28/the-origin-and-development-of-the-energy-principle/

Copyright © 2008 John Schmitz


[1] Hermann von Helmholtz (1821-1888) reported on July 23 in 1847 on the principle of conservation of energy and showed that he had acquired a deep understanding of this principle. He was, together with Rudolf Clausius, the founder of what was called the Berlin School of Thermodynamics where he succeeded Magnus as the director of the Physical Institute. The influence of this school on the development of thermodynamics was crucial. It is almost unbelievable how many famous scientists were connected to this school. To name a few: Walter Nernst, Max Planck, Albert Einstein, Erwin Schrödinger and Leo Szilard.

[2] Although Helmholtz himself had a very good knowledge of mathematics

[3] See for instance: http://www.bartleby.com/30/125.html

[4] Work is simply defined here as lifting a weight.

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