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adopted angle of incidence angle of refraction annular apparatus Argand Argand lamps arrangement Augustin Fresnel beam Bell Rock belt burner catadioptric catoptric centre of curvature colza oil concave cone conoïd construction convex course curve curved mirrors cylindric diameter dioptric light direction divergence Eddystone edge effect equal feet fixed lights flame flashes focal distance frame Fresnel frustum glass grinding height High Holborn illumination inches Inchkeith inclination instrument lamp lantern length lens lenses Light-room Lightkeeper loss of light luminous means millimètres mode Northern Lighthouses observer obtained outer parabolic paraboloïdal mirror parallel passing placed plane position principal focus prisms produced radius of curvature reflecting side reflecting surface reflectors refractive index refractors revolving lights rings Robert Stevenson round screws shadows shews sin² Skerryvore spermaceti spherical tance tangent tion tower triangle tube vertex vertical axis wick
Page 148 - length, but divided into three or four pieces ; the lower end of each of these pieces for about 1£ inch is opened out into a conical form, about 5£ inches in diameter at the lowest part. When the chimney is put together, the upper end of the bottom piece is inserted about
Page 36 - It consists of a central belt of refractors, forming a hollow cylinder 6 feet in diameter, and 30 inches high ; below it are six triangular rings of glass, ranged in a cylindrical form, and above a crown of thirteen rings of glass, forming by their union a hollow cage, composed of polished glass, 10 feet high and 6 feet in diameter ! I know
Page 11 - the sea prevented any one going down to the rock, anxiously looking for supplies from the shore, and earnestly longing for a change of weather favourable to the recommencement of the works. For miles around nothing could be seen but white foaming breakers, and nothing heard but howling winds and lashing waves.
Page 178 - When stores of any kind are to be landed for the use of the Lighthouse, the Lightkeepers shall attend and give their assistance. The Principal Lightkeeper must, upon these occasions, satisfy himself, as far as possible, of the quantity and condition of the Stores received, which must be duly entered in the Store-book and Monthly Return-book.
Page 7 - successively. The machinery, which causes the revolution of the frame containing the lamps, is also applied to tolling two large bells, in order to give warning to the mariner of his approach to the rock in foggy weather. The erection of the Bell Rock Lighthouse cost £61,331, 9s. 2d.
Page 36 - was to that of the seven upper tiers of mirrors of the first order, as 140 to 87. Nothing can be more beautiful than an entire apparatus for a fixed light of the first order,
Page 173 - The Lightkeepers shall keep a regular and constant Watch in the Light-room throughout the night. The First Watch shall begin at sunset. The Lightkeepers are to take the Watches alternately, in such manner that he who has the first Watch one night shall have the second Watch next night. The length or duration of the
Page 115 - sufficient to discourage us from attempting to improve the visibility of fixed lights in the manner proposed by Captain Hall, even supposing the practical difficulties connected with the great centrifugal force generated by the rapid revolution of the lenses to be less than they really are.