At the end of the sixteenth century astronomers and others felt compelled to choose among different cosmologies. For Tycho Brahe, who played a central role in these debates, the intersection of the spheres of Mars and the Sun was an outstanding problem that had to be resolved before he made his choice. His ultimate solution was to eliminate celestial spheres in favour of fluid heavens, a crucial step in the abandonment of the Ptolemaic system and the demise of Aristotelian celestial physics. These debates involved issues that had not previously been part of astronomy, and had the effect of undermining the traditional hierarchy of the sciences. While this complicated story involves many scientific personalities of the sixteenth and seventeenth centuries, in the present paper we will concentrate on one figure who has been assigned an unnecessarily minor role in most histories of science: Christoph Rothmann. In the present paper we show that ‘the dissolution of the celestial spheres’ depends on arguments about the substance of the heavens, following a mistaken argument of Gemma Frisius, elaborated by Joannes Pena and appropriated by Rothmann. We next consider the status and origin of the doctrine, as presented by Brahe, that the heavenly spheres are solid, and the impact on Brahe of Rothmann's treatise on the comet of 1585. Rothmann provided several key ideas that enabled Brahe to develop his system, and we suggest in passing that Rothmann may also have precipitated Brahe's re-evaluation of his attempt to detect the parallax of Mars during the opposition of 1582–83. We offer a new account of this central piece of evidence for the Tychonic system.

With the coming of the French Revolution in 1789 and its attack on monarchy, the landed aristocracy, the religious establishment and religion itself, and especially with the coming of the sans culottes and the First French Republic and its ‘Terror’ in 1793–94, fear of revolution swept the British establishment. Sensing revolution everywhere, successive Tory governments, rooted in the alliance of the Church of England, the landed aristocracy and the monarchy, practised a consistent and harsh policy of repression. Neither the fear nor the repression eased with the arrival of, or indeed, with the departure of, Napoleon who, as Emperor from 1804 to 1815, seemed determined to conquer Britain by means of revolutionary propaganda, economic blockade and/or military invasion.

By 1918, four years of total war had produced a complete mobilization of scientists, scholars and their institutions throughout Europe, the British Empire, and the United States. Public men spoke freely of the implications of a ‘technological war’ run by engineers and chemists. And in the years following the Armistice, historians were eager to record the achievements of the professions, and the effects of the war on their self-image. Memories of the First World War, as Paul Fussell reminds us, remain and shape the texture of our daily life. The parapet, wire and mud have become permanent features of human existence. In a similar way, the war of 1914–18 had enduring consequences for science and scientists, rarely appreciated until the end of the Second World War. Scholars and savants deserted their classrooms for the trenches, industries and war offices, while professional bodies turned themselves into useful extensions of military departments. By October 1914, the infamous Professors' Manifesto, with its Appeal to the Cultured Peoples of the World had identified German science with German war aims, and the natural sciences were fully at war. Scientific knowledge applied to the war was – at one and the same time – a fulfilment of the Enlightenment project of reason, and a violation of the Enlightenment ethos of humanism and internationalism.