Science has not always been based upon philosophical naturalism: theistic methodology was central to scientific practice in Britain throughout the nineteenth century, and it produced results. Indeed, theists and naturalists had many common methods and aims, despite their differences over metaphysics. However, science eventually became linked to naturalism—indeed, became a kind of “church” to naturalism—through Thomas Huxley's back-door strategies of training science teachers, writing textbooks, and shaping the setting and marking of examinations. Having obtained the institutional means of doing so, methodological naturalists not only dictated what was to count as science but also rewrote history to make it seem that there had never been another way. So runs the argument of this new study from Matthew Stanley, Huxley's Church and Maxwell's Demon.

In the mid-nineteenth century, theistic science dominated, operating under practices, if not presumptions, that were only later claimed to be exclusive to scientific naturalism. For instance, uniformity, which underpinned not only the presumed persistence and consistency of natural law but also the ability to reason by analogy, was fundamental to a theistic world view, as evidenced in the work of Baden Powell, Charles Lyell, Charles Babbage, and William Whewell as well as James Clerk Maxwell. Assumptions about the limitations of science were also fundamental to theistic thought. Evangelical calls for humility in the face of divine mystery and the belief that the First Cause was not appropriate for scientific investigation could be harmonized with Huxley's belief that there were things beyond human comprehension. Theists and materialists had aims as well as ethics and methods in common, and Huxley collaborated with theologian Frederick Maurice to ensure the success of the Working Men's College, each assuming the moral benefit of a scientific education.

It was only in the growing attention to the science of mind that tensions became apparent. If natural law was all encompassing, then it must also account for the human mind. To Huxley the implications were clear: humans were automata, free will was an illusion, and mind was a function of matter. Maxwell's approach to free will, by contrast, was framed by his evangelicalism. Following Maurice, Maxwell believed free will was central to the acceptance of God's grace, but physics presented him with metaphysical problems. In light of the second law of thermodynamics and W. B. Carpenter's work in psychophysiology, Maxwell admitted that the days of unlimited action for free will were over. Further, if the eternal soul was proposed as the locus of the will, then there were tensions between an eternally acting force and the presumption of entropy.

In attempting to reconcile this problem Maxwell turned to Balfour Stewart's two distinct types of mechanical systems. Although stable systems were well known and thoroughly determinable, unstable systems were less predictable; in them, even barely perceptible forces might have significant effects. Initially, Maxwell found this line of investigation compelling; the soul was not an engine of action, but a delicate force initiating a larger process. Ultimately though, Maxwell recognized that even a tiny persistent force in a closed system would eventually run down, and with this acknowledgment his hopes for explaining an eternal soul this way diminished. Discoveries in French mathematical physics, on the other hand, seemed to offer a resolution: “singular states” in molecular physics revealed that entire families of solutions sometimes overlapped, making it quite impossible to predict which direction a particle might take. Maxwell incorporated these insights into his 1873 address to the British Association, in which he decried materialist attempts to apply what little they understood of dynamics to questions of biology to rule out anything other than a mechanist account of volition and sensation. Huxley, Herbert Spencer, Carl Nägeli, and Emil Du Bois-Reymond were his targets here. Notably, while Maxwell was eager to find an account of free will that was compatible with physical science, he also rejected the attempts of those such as John Drysdale, who sought to justify its existence, and that of the soul, in mechanical terms. Our knowledge of the soul, he argued, like our confidence in our own volition, were founded upon our conscious experience. Thus, while the soul and its expression through willed actions were outside the explanatory reach of physical science, they could not be ignored by science because their effects changed the outcomes of otherwise predictable systems.

Maxwell's efforts to defend free will also advanced his scientific research. His conviction that there must be certain unstable systems within which the second law of thermodynamics did not always apply led him to develop what became known to his contemporaries in kinetic theory as “Maxwell's demon.” Under conventional wisdom, given two connected vessels, each filled with gas at different temperatures, over time the temperature of the whole would achieve equilibrium. However, Maxwell maintained that this need not be the case. If some hypothetical being—much more acute and skilled to the task than any human, but by no means a supernatural entity—were able to calculate the paths and the velocities of all the gas molecules and could close off the connection to prevent the passage between the two vessels of slower, colder molecules, then a buildup of faster molecules in one vessel, and thus an increase of heat, would be the result—that is, a flow of heat from the colder vessel to the hotter one. Because he imagined the connecting closure would have no mass, and that its operation would require no physical work, he concluded that the second law could, at least hypothetically, be violated.

Many other case studies might be mentioned, Stanley argues, but Maxwell's writings illustrate how mid-Victorian scientific and religious thought could intermingle in ways that later came to seem impossible. By the century's end, British science was Huxley's church—materialism was the modus operandi, and theists were summarily excommunicated. The previously shared ideals of uniformity and the limits to scientific knowledge were reframed as exclusively materialist presumptions. Indeed, John Tyndall and Huxley rewrote history; Tyndall cast Michael Faraday's Sandemanian beliefs as incidental to, rather than central to, his science, while Huxley portrayed Carpenter's psychophysiology as the very underpinning of mechanism despite Carpenter's opposition to these conclusions. Finally, it was Huxley, Tyndall, and their students who framed the training of the next generation of scientists.

Stanley's book is a good one—his setting up of Huxley and Maxwell as representatives of materialism and theism works well to demonstrate his thesis (even if, ironically, it makes the story seem too Manichean) and provides insight into the nature of nineteenth-century science. Historians have long rejected the overly simplistic “warfare thesis,” and Stanley again shows us why, but he also shows us that we should not overlook the very real campaign to win science for materialism that Huxley, Tyndall, and others waged by means of the opportunities before them as well as of the complacency of their theistic rivals. If I have one criticism, it is that the cast of supporting characters, Maurice, William Thompson, Drysdale, Tyndall, Spencer, Lyell, Carpenter, Nägeli, Du Bois-Reymond, and more, remain too far in the background. To bring them forwards would be more satisfying for this reader and would only strengthen Stanley's thesis.