Tycho Brahe has often been viewed as an unicum, a singularity. On the one hand, he is known as a dedicated astronomer who invented fine and precise instruments; on the other, he is a vain, quarrelsome, jealous, overbearing and secretive nobleman. Adam Mosley endeavours to disprove some parts of this picture, to show, as he phrases it, that Tycho Brahe ‘was only one astronomer among many, even if he was described as a prince’ (p. 297). Mosley sets out to do this by examining the people, letters, books and instruments by which astronomical knowledge, patronage and quarrels moved, in order to reconstruct the membership, norms and practices of the astronomical community of which Tycho was a part. By mapping the circulation of letters, books and instruments, Mosley demonstrates that the making of astronomical knowledge was dependent on the exchange of these material objects; that it was collaborative, as members traded and calibrated observations, contested timekeeping practices and argued about the shape of the cosmos; and that it was embedded in a system of patronage and gift-exchange. Mosley does all this mainly through an intensive study of Tycho Brahe's correspondence. His letters reveal the Danish nobleman to have been part of a community, made up of nobles, scholars and instrument-makers, with their attendant couriers (of letters, instruments and news), merchants and others. Moreover, Tycho's striving for fame and patronage was hardly unusual at this time, and his vanity and peevishness can be read in this context. In all, Mosley shows how deeply Tycho was struggling to reform astronomy, especially in his concern for precision in observation and timekeeping.

Mosley provides a persuasive account of the ways that the exchange of letters; the printing, reading and exchange of books; and the circulation of instruments made knowledge. He is particularly enlightening on the ways that instruments mediated knowledge in his examination of technology and knowledge transfer between Hveen and the Landgrave of Hessen-Kassel's court, and between Tycho's island observatory and globemakers across Europe. He illustrates the ways that instruments and instrument-makers were central in the making of astronomical knowledge, and he includes an interesting discussion of the extent to which calculating devices such as astrolabes, orreries and mechanical models of the universe were understood to function as models of the cosmos, rather than simply as calculating machines. He makes clear that whatever else they may have represented, instruments were valued as both intellectual and material objects, and, as such, they stimulated much debate and discussion about the cosmos.

Because so much has been written on Tycho Brahe, Mosley is at pains to correct and refine many of the long-entrenched notions about, for example, when Tycho first took up the geo-heliocentric model, when he stopped believing in solid crystalline spheres on which the planets revolved, how badly he really behaved in the affair over priority and intellectual property with Ursus, and so on. While these nuggets of scholarship are no doubt of great value especially to historians of astronomy, Mosley's methodological points about employing scientific correspondence, books and instruments to map out an era's scientific culture will prove of interest to historians of science more generally.

A great deal of effort and industry is evident in this book, and it contains a wealth of information for historians, particularly of sixteenth- and seventeenth-century astronomy. But it is also full of wonderful details that reflect on early modern material life and scientific culture, such as the precariousness of the exchange of letters, the frustration such delay engendered in letter writers eagerly awaiting information about astronomical phenomena, the difficulty of printing mathematical books in the sixteenth century, the ambivalence about the problems and potential of the printing press and the printed word, and the hot pursuit by early modern scholars of volumes containing astronomers' marginal notations. Mosley's claim that historians of science should attend to the material culture and practices of astronomy is very well taken, and the fruits of such an approach are borne out in his book.