This paper sets out to examine the changes which took place in Thomas Young's concepts of the ether between 1799 and 1807. During the earlier part of this period he supposed the ether to consist of mutually repelling subtle particles which are attracted to particles of matter. Hence, he considered that the ether is denser within dense bodies than in rare ones. Furthermore, Young proposed that the ether density does not change abruptly at an interface; instead the denser ether extends (...) beyond the geometrical limit of a body to form an atmosphere around it. As this hypothesis of an atmosphere of dense ether surrounding material bodies will be the central subject of this paper, I shall in future refer to it as the ether distribution hypothesis. (shrink)

This paper reconstructs what may have led the American professorof chemistry andnatural philosophy John William Draper to introduce a new kind ofradiation, whichhe dubbed `Tithonic rays''. After presenting his and earlierempirical findings onthe chemical action of light in Section 3, I analyze his pertinentpapers in Section 4with the aim of identifying the various types of argumentshe raised infavor of this new actinic entity (or more precisely, this newnatural kind of raybesides optical, thermal and perhaps also phosphorogenic rays).From a modernperspective, all (...) of these obviously belong within theelectromagnetic spectrum,but not so for many thinkers of the 19th century. I close withremarks about whyDraper''s interpretation was abandoned in the second half of the19th century (hehimself recanting only in 1872), and why I think such a naturalhistory ofargumentation (as one might call my approach in Section 4) may beuseful for acomparison-oriented history of science. (shrink)

In his comprehensive survey of the work of William Herschel, published in the Annuaire du Bureau des Longitudes for 1842, Dominique Arago argued that the life of the great astronomer ‘had the rare privilege of forming an epoch in an extended branch of astronomy’. Arago also noted, however, that Herschel's ideas were often taken as ‘the conceptions of a madman’, even if they were subsequently accepted. This fact, commented Arago, ‘seems to me one that deserves to appear in the history (...) of science’. From the time Herschel published his first paper in the Philosophical transactions in 1781, he was subjected to the suggestion of lunacy. His patron and friend William Watson, told him that after his claims for the extraordinary power of his telescopes, ‘your prognosis that some would think you fit for Bedlam has been verified’. On learning of Herschel's supremely accurate new micrometer, the astronomer Alexander Aubert exclaimed to Herschel that ‘we would go to Bedlam together’: Aubert wrote to Herschel in January 1782 that he should ‘mind not a few jealous barking puppies: a little time will clear up the matter, and if it lays in my power you would not be sent to Bedlam alone, for I incline much to be of the party’. (shrink)

As a natural philosopher, Count Rumford is best known for his vehement advocacy of a motion or mechanical hypothesis of heat and for the dramatic experiments that he performed to support this hypothesis. Although a motion hypothesis which held that heat was merely the motion of the ultimate particles of a body had a distinguished history, with advocates that included Bacon, Boyle, Hooke, and Newton, most British natural philosophers by the beginning of the nineteenth century believed that the phenomena associated (...) with heat were caused by an imponderable fluid. William Henry reflected contemporary opinion in 1803, when he wrote:The former of these opinions [i.e. the existence of caloric], though far from being universally admitted, is now generally received; and the peculiar body, to which the phenomena of heat are referred, has been denominated by M. Lavoisier [as] caloric. (shrink)