William Tobin

Foucault's invention of the silvered-glass reflecting telescope and the history of his 80-cm reflector at the observatoire de Marseille

Abstract Leon Foucaults serendipitous development of the silvered-glass reflecting telescope is described. Foucaults largest mirror had an 80 cm diameter and was installed under the clear skies of Marseilles in 1864. The story of this telescopes hundred years of service is sketched out; famous observers with the instrument were Stephan, Fabry and Jonckheere.

Toothed wheels and rotating mirrors: Parisian astronomy and mid-nineteenth century experimental measurements of the speed of light

Abstract The speed of light was first shown to be finite by Romer in 1676 at the Paris Observatory. A century and a half later the Observatory was again a centre of research on the speed of light—but this time in the laboratory or across Paris. Arago and Le Verrier, successive Observatory directors, encouraged Foucault, Fizeau and Cornu to rotate mirrors or spin toothed wheels. In an experiment devised by Arago, light was found to travel faster in air than water, completely demolishing the corpuscular theory, which had already been undermined by a number of physical experiments and astronomical observations. Subsequent absolute measurements supported the lower value for the speed of light and smaller distance to the Sun suggested by Le Verriers analysis of solar-system motions.

Alfred Donné and Léon Foucault: the first applications of electricity and photography to medical illustration.

The first electric projecting microscope and the first published photomicrographs harnessed recent technological developments to provide improved methods of medical illustration for educational purposes. Both projects were the work of two Frenchmen. The impetus came from the microscopist Dr Alfred Donné (1801–78), discoverer of trichomonas vaginalis and leukaemia. Implementation was primarily by his medical‐student assistant, Léon Foucault (1819–68), who later gained fame as a physicist, especially with his pendulum demonstration of the Earth’s rotation.

The variable Ca II absorption in ? Pictoris during 1998

Variable absorption features were observed in the visible and ultraviolet spectrum of beta Pictoris soon after this star gained attention in the early 1980s due to its large IRAS infrared excess and the discovery, from optical imaging, of an edge-on dust disk. The absorption has been attributed to the evaporation of infalling planetesimals or comet-like bodies (the falling evaporating bodies, or FEB, hypothesis). With a view to confronting this hypothesis with fuller observations, we monitored the CaII H and K lines in beta Pictoris simultaneously during 1998, obtaining sequences of spectra on 50 nights. Variable absorption was usually present. The different oscillator strengths of the H and K lines permit the determination of covering factors, but detailed modelling is required to test whether all features can be explained by the FEB hypothesis. The blend of CaII H with Balmer HII means that the H and K photospheric profiles are different, and that the variable absorption features do not evolve in parallel. The behaviour of the variable absorption on November 27 is evocative of a body passing in front of the stellar disk in a prograde equatorial orbit.

The Mt John programme of CCD photometry of eclipsing binaries in the magellanic clouds

This paper reviews recent progress in CCD photometry of eclipsing binary systems in the crowded fields of the Magellanic Clouds. Some preliminary findings are given. The interesting eccentric system HV2274 is noted as important for follow-up studies, particularly concerning its apsidal motion. Some further developments are anticipated.