In Light without Heat, David Caroll Simon proposes a new interpretation of scientific inquiry in the early modern period, which he calls “the observational mood.” This mood is characterized by unselfconsciousness, carelessness, and mental laxity. Additionally, it is synonymous with “disinvoltura,” “nonchalance,” or “indifferency” (2). In this way, Simon is departing from the general view that takes the scientific method to be a firm constraint on both the practice and the mind of the natural philosophers. He argues that, compared with the so much praised scientific method, the observational mood constitutes a better antidote against false theories and against passions that prejudice the sciences. The condition for entering this mood is to move attention from the self and its feelings to the exterior world of sounds and sights. This switch to the exterior has the advantage of overcoming arising technical difficulties. However, even if Simon considers this more effective than the rigorous scientific method, the observational mood is in fact an interruption of whatever happens (during the scientific investigation), an interruption during which both attention to rigor and its abandonment are joined. The scope of the book, as explained in the introduction, is not to find the coherent relation between the method and the observational mood. This is because, as Simon argues, the observer and the theorist have different aims: “what I think I want from a natural-philosophical investigation might have little to do with what in fact happens when I surrender to the observational mood” (21). Simon aims only to know what happens.

The book contains four chapters, with a comprehensive introduction and a postscript. The introduction gives an account of the observational mood, draws a comparison between this new interpretation and current literature on early modern scientific method, and describes the book's methodology—the interplay of literary and philosophical texts. Each of the first three chapters bring together two authors, one seen now as a representative of “science” and one of “literature,” while the last chapter focuses on only one author, Milton. With the exception of the first chapter, which sets the framework for those that follow, the remaining three chapters are each composed around one concept: thought, vision, and trial, respectively.

In the first chapter, “‘Nonchalance’ and the Making of Knowledge,” Simon uncovers the influence of Michel de Montaigne on Francis Bacon's science. Carelessness is present in Bacon's works in the capacity to easily change the topics of research, the delight of pursuing knowledge, and self-presentation. Against Montaigne, Bacon emphasizes the importance of self-improvement, and Simon considers Bacon's description of the effortlessness of self-discipline as being his main argument against the current scholarship which emphasizes the strict method. However, he focuses on the literary works more then on the scientific ones and this might facilitate a reading in which the rigor of the method is not at stake.

In the next chapter, “The Angle of Thought,” Simon focuses on the natural philosopher Robert Boyle and the writer Izaak Walton. Simon argues that Boyle's “way of thinking,” which makes possible sudden and unexpected revelations in both scientific and religious contexts, can be called “nonchalance” and is characterized by the cognition following “the winding path of errant association” (83). In Walton's poem The Compleat Angler (1653), Simon finds echoes of the Baconian program in the continuity between the pastoral tranquility and the trials of knowledge productions. Both authors, though in different contexts, share a similar understanding of nature as various, and thus they both find value in cognitive suppleness.

Andrew Marvell and Henry Power are the protagonists of the third chapter, “The Microscope Made Easy.” In respect to one of the most important instruments of the early modern natural philosophy, Simon analyses the literary life of one of the phantasies created by the microscope: effortless accessibility and visual pleasure. Reading Power's Experimental Philosophy (1664) through Marvell's “Upon Appleton House,” (1651) Simon shows that the observational mood is a way of seeing, too, as well as of thinking, as this is the consequence of the microscope's appeal to the imagination.

In the last chapter, “The Paradise Without,” Simon analyzes the practice of gardening performed by Adam and Eve in paradise, as depicted by Milton is his Paradise Lost. Simon argues that the prelapsarian labor was a game and in consequence this labor led to the feeling of easygoingness, the equivalent of the observational mood. Moreover, he claims, Milton's aim was to bring paradise to the readers by identifying two places that seem very different: there (Paradise) and here (the postlapsarian world): “Perhaps Paradise is a name for everywhere you don't know very well—anywhere you can only come to know through wide-ranging exploration” (209). The minimal conditions to attain the observational mood and the lost innocence are, in Simon's reading of Milton, soft emotion and a wondering mind.

This book offers an innovative reading of some well-known early modern literature and philosophy. However, one potential criticism lies in the fact that Simon claims that he is more interested in practice, or in “what happens,” but in fact there are few instances when he analyses proper scientific practice. Nevertheless, one has to admire Simon's original coupling of authors and his sharp argumentation. It is relevant that Simon anticipates critical objections by explaining his relation to the authors he studies: “What I have to say about the observational mood is dependent on my seventeenth-century sources (I wouldn't know how to say it without them), but they've had to enlist my participation in unfolding their ideas—not because they're guilty of failure or incompleteness but because they don't take my subject as their focus” (25).