Heat¶
Core Argument¶
In this chapter, Engels traces the dialectical relationship between mechanical motion and heat, arguing that the transformation of motion between these forms is not merely a physical process but a historical and theoretical one with profound implications for understanding nature. He begins by distinguishing two forms in which mechanical motion (vis viva) disappears: first, into mechanical potential energy, which is a reversible process capable only of being reconverted into mechanical motion; second, into friction and impact, where motion is lost as such and transformed irreversibly into qualitatively different molecular motions—heat, electricity, and light. Friction and impact, he notes, differ only in degree, with friction being chronic impact and impact acute friction. This transition from the motion of masses (mechanics) to molecular motion (physics) marks a critical boundary in the hierarchy of natural science.
Engels then expands the scope of physics, acknowledging that contemporary physics includes phenomena like ether vibrations (light and radiant heat) and electricity, which are not strictly molecular motions. He references Clausius’s Mechanical Theory of Heat to note that ether may participate in molecular movement, but concedes that knowledge of the ether remains limited; once mechanics of the ether is developed, much of physics will be subsumed under it. The chapter argues that only with molecular motion does the change of form of motion acquire full freedom: heat converts to electricity in the thermopile, becomes identical with light at certain radiation stages, and reproduces mechanical motion; electricity and magnetism transform into each other and into heat, light, and mechanical motion, all in definite measurable relations.
Engels then turns to the historical discovery of these conversions. The making of fire by friction, he asserts, was humanity’s first victory over non-living nature, pressing natural forces into service. He contrasts the enduring cultural memory of this discovery—evidenced by rituals requiring sacred fire to be produced by friction, from Jewish circumcision with stone knives to German bonfires against epidemics—with the forgotten significance of earlier tools. However, this process was one-sided: mechanical motion converted to heat. The dialectical completion required the reverse—heat converted to mechanical motion—which took millennia, from Hero of Alexandria’s steam-powered machine (c. 120 BC) to the first practical steam engine. Engels presents the steam engine as the first truly international invention, crediting Papin (with Leibniz’s key idea of cylinder and piston), Savery, Newcomen, and finally Watt’s separate condenser.
The chapter concludes with a polemic against the theoretical backwardness of physicists. Despite abundant travel accounts of friction fire-making and the steam engine’s development, physicists remained indifferent until Sadi Carnot took up the problem in the 1820s. Carnot nearly solved it, but was hindered not by lack of data but by a preconceived false theory—the notion that heat, light, electricity, and magnetism were imponderable substances. Engels stresses that this error arose not from philosophy but from the physicists’ own naturalistic mode of thought, which he implicitly contrasts with dialectical materialism. The chapter thus argues that practice (technology) outstripped theory, and that only a dialectical understanding of motion’s transformations—rejecting the substance theory of heat—could complete the scientific picture.