In June 1849 William Thomson (Later Lord Kelvin) wrote to Michael Faraday suggesting that the concept of a uniform magnetic field could be used to predict the motions of small magnetic and diamagnetic bodies. In his letter Thomson showed how Faraday's lines of magnetic force could represent the effect of the ‘conducting power’ for magnetic force of matter in the region of magnets. This was Thomson's extension to magnetism of an analogy between the mathematical descriptions of the distribution of static electricity and of the diffusion of heat through uniform bodies. In 1850 Faraday published his first comprehensive theory of the magnetic properties of matter. He explained the behaviour of matter in the field by four assumptions: that matter has a specific disturbing effect on the normal distribution of lines of magnetic force; that this effect depends on its ability to conduct or transmit the magnetic action; and that material bodies tend to move so as to cause the least possible disturbance of the lines from their normal distribution. Faraday also assumed that diamagnetics transmit magnetic action less well than empty space, while paramagnetics transmit it more readily than space. This implied that space must have a specific conductivity between that of paramagnetic and diamagnetic materials. In order to preserve a distinction between matter and space Faraday defined ‘matter’ as either the source of action or as a conductor which is able to influence the lines of action; space was the absence of such powers. While space could conduct, it differed from matter in that it could neither originale lines of force nor influence their course and distribution.

In 1826 André-Marie Ampère published the ‘Mathematical theory of electrodynamic phenomena, uniquely derived from experiment’, in which he showed how the mathematical law for the force between current elements could be derived from four ingenious equilibrium experiments. He made a great show of following a Newtonian inductivist methodology, and his law, like Newton's for gravitation, was presented as a purely descriptive mathematical expression for a certain class of phenomena, one for which its author did not provide any causal or ontological justification. Ampère's electrodynamics would accordingly seem to have been a solid contribution to the Laplacian-Newtonian approach to physics so actively pursued in France during the first quarter of the nineteenth century. It does not surprise us to read that his electrodynamic force law and his molecular-currents theory of magnetism were immediately and widely accepted by his French contemporaries. Ampère was, in this view, just another of the many great French mathematical physicists of the period.

A recent note by lan Inkster observed that a Parliamentary Act of 1817 to suppress seditious meetings also posed a threat to scientific lecturers and societies between 1817 and 1820. Further evidence is presented here as to the intentions of the 1817 Act and its effects on science. It is particularly important to add to the observations of Inkster, first, that chartered societies were exempt, and second, that the Act expired on 14 July 1818, although further measures were introduced in December 1819. To explain the provisions of these Acts, especially the distinctions made between lectures held by chartered societies as opposed to independent associations, it is relevant to consider how legislation to prevent seditious meetings and societies in the wake of the French Revolution demarcated between seditious blasphemy and legitimate scientific inquiry. The Acts provide an opportunity of locating science in contreversies over the freedom of speech and association. The questions arise of the relation of the 1817 Act to legislation of 1795, 1799, 1801, and 1819 which imposed licensing on lectures, and of the extent to which repressive legislation inhibited the activities of lecturers and societies. The intellectual repercussions were of such magnitude that the mathematician de Morgan observed in retrospect, ‘From 1815 to 1830 the question of revolution or no revolution lurked in all our English discussions’.