Kenneth L. Caneva, <i>Helmholtz and the Conservation of Energy: Contexts of Creation and Reception</i> Cambridge, MA: MIT Press, 2021. Pp. 760. ISBN 978-0-262-04573-5. $125.00 (hardcover).

The principle of the conservation of energy was a pivotal advance in nineteenth-century physics, ushering in a new understanding of the discipline and reshaping its status.Diverse subjects began to merge into a unified domain centred on the concept of energythe precise definition of which was elusive.Helmholtz, a master of physics and mathematics and the chief architect of modern physiological optics, formulated, in his seminal 1847 essay On the Conservation of Force, what became known as the principle of the conservation of energy.Notably, he did this without a clear general concept of energy in mind, as the term 'force' in his title suggests.Kenneth L. Caneva retraces the intricate path leading to the development of the conservation of energy, focusing on Helmholtz's significant contributions to the subject.Caneva does not dwell on the debates over precedence or Helmholtz's broader achievements as a scientist.Instead, he explores the sources Helmholtz drew upon, what he thought he had achieved, and how his perspective evolved.This evolution was influenced by responses, critiques, the parallel contributions of contemporary scientists and the gradual introduction of the principle into textbooks, thereby becoming part of established science.Caneva relied on an enormous corpus of primary and secondary documents, published and unpublished, to address these topics and organize them into a coherent set of chapters.The first five chapters provide a detailed examination of Helmholtz's seminal 1847 essay and the intellectual milieu in which it originated.Caneva begins by delineating the central inquiries that motivated Helmholtz to compose his memoir.Subsequently, the author explores recurring topics and debates that resonate in Helmholtz's contemporary reception, such as the impossibility of constructing a perpetuum mobile, physiological questions related to the origin of animal heat, molecular and material theories of matter and motion, philosophical considerations of causality and the nature of force.After outlining the broader and immediate context leading to Helmholtz's essay, Caneva proceeds with a detailed examination of the essay itself.He delves into how Immanuel Kant's ideas influenced Helmholtz's formulation of the conservation of forcea topic that has received considerable scholarly attention.Well aware of the complexity of the topic, Caneva builds a narrative that highlights interrelations among various themes, such as the concept of heat as a form of motion and its relation to the principles of mechanics.He then illustrates the multiple intentions behind Helmholtz's essay and examines how Helmholtz's understanding of his work evolved.Initially motivated by the need to determine the relationship between the forces of nature that make a