L'encyclopédie Britannica ; un dictionnaire des sciences, des arts, de la littérature et de l'information générale . e au l'Observatoire Radcliffe à Oxford, dans l'année 1850, Introduction, p. iii. * L'illumination de ces échelles est intéressant comme étant l'firstapplication d'électricité pour l'éclairage des instruments astronomiques. Mince fil de platine a été rendue par un voltaiccurrent à incandescence ; une petite lampe électrique à incandescence serait maintenant foundmore satisfaisante. moyen de mesurer le point focal ont été fournis ; symmetricalmotion a été donné aux glissières ; échelles sur chaque diapositive ont été providedinstead de sc

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The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . e at the Radcliffe Observatory, Oxford, in the Year 1850, Introduction, p. iii. * The illumination of these scales is interesting as being the firstapplication of electricity to the illumination of astronomical instru-ments. Thin platinum wire was rendered incandescent by a voltaiccurrent; a small incandescent electric lamp would now be foundmore satisfactory. means of measuring the focal point were provided; symmetricalmotion was given to the slides; scales on each slide were providedinstead of screws for measuring the separation of the segments, andboth scales were read by the same micrometer microscope; ametallic thermometer was added to determine the temperature ofthe scales. These small instruments have since done admirablework in the hands of Schur, Hartwig, Kustner, Elkin, Auwers andothers. The Russian Government ordered three new heliometers (each of4 in. aperture and 5 ft. focal length) from the Repsolds, and thedesign for their construction was superintended by Struve, Auwers. Fig. 9. and Winnecke, the last-named making the necessary experiments atCarlsruhe. Fig. 9 represents the resulting type of instrument whichwas finally designed and constructed by Repsolds. The brass tube, strengthened at the bearing points by strong truly turned collars, rotates in the cast iron cradle 5 attached to tha declination axis, o is the eye-piece fixed in the optical axis, b the micrometer for readingboth scales, c and d are telescopes for reading the position circle p, e the handle for quick motion in position angle, / the slow motion mposition angle, | the handle for changing the separation of thesegments by acting on the bevel-wheel e (fig. 10). fc is a milledhead connected by a rod with h (fig. 10), for the purpose of inter-posing at pleasure the-prism ir in the axis of the reading micrometer;this enables the observer to view the graduations on the face of themetallic thermomet

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