In light of research which, since the publication of Rousseau and Porter’s Ferment of Knowledge, has demonstrated the continued centrality of magic and the occult to what may be termed “scientific knowledge” in the early modern period, this essay argues that one domain of practice where these concerns remained paramount well into the eighteenth century is the consumption of recipes. Whether exchanged between individuals or collected in print format, these mobile informational media relied on forms of proof under­pinned by personal (...) experience and collective accreditation, with an inductive and empirical focus that was distinct from Cartesian deduction. Because the culture of recipe exchange was so widespread, encompassing scholars, savants and lay readers, secrets offered ways to challenge strict mechanistic interpretations in favour of a view of the natural world as informed by unseen active powers, particularly where the virtues of materials such as magnets or medicinal simples were concerned. Using private library catalogues of book owners, a commonplace book and a scientific periodical produced in France during the decades after 1700, the article traces the way secrets culture continued to foster an epistemological space in which mechanical explanations evidently fell short of accounting for quotidian experience. (shrink)

We investigated the current-voltage I(V) characteristics of GaAs/AlAs double-barrier heterostructures. A fine periodic structure of the resonant tunnel current has been revealed. We attribute it to a sequence of the collective excitations, presumably of the coupled plasmon-phonon type, that are induced in the heavily doped collector region by hot electrons which escape from the quantum well. An oscillatory structure appears also in the valley regions of the I(V) curve under a high magnetic field parallel to the current. It is due (...) to the off-resonance tunnelling between the Landau-quantized states of the emitter and quantum well. Particular phonon-assisted processes in the tunnelling have been identified. (shrink)