Hydrostatics and pneumatics / [Dionysius Lardner].

  • Dionysius Lardner
Date:
1831
Catalogue details

Licence: Public Domain Mark

Credit: Hydrostatics and pneumatics / [Dionysius Lardner]. Source: Wellcome Collection.

    365/376 (page 349)
    glass lenses for the admission of light, such as are used in the decks of vessels to illuminate the apartments below. The shape of the machine is generally oblong, with seats for the diver at the end, shelves for tools, writing materials, or any other articles necessary to be carried down, are placed at the sides; and below the seats there are hoards placed across the machine to support the feet. Messages are communicated from below to above either in writing or by signals. A board is carried in the bell on which a written message may be chalked. This board communicates by a cord with the arm of the su- perintendent above, who, on a signal given, draws it up, and who, in a similar way, is able to return an answer. When the bell is of cast iron, a system of signals may be made by very simple means : a blow struck by a ham- mer on the bell produces a peculiar sound distinctly au- dible at the surface of the water, and which cannot be mistaken for any other noise. The number of strokes made on the bell indicate the nature of the message, the smaller number of strokes signifying those messages most frequently necessary. Thus, a single stroke calls for a supply of fresh air; two strokes command the bell to stand still ; three express a desire to be drawn up ; four to be lowered, and higher numbers express motion in different directions. Of course this system of signals is arbitrary, and liable to be varied in different places. The bell is usually suspended from a crane, which is placed above the surface of the water, and in order to move it this crane is placed on a railway, by which it is enabled to traverse a certain space in one direction. The carriage which traverses this railway supports another railway in directions at right angles to it, on which the crane is supported. By these means two motions may be given to the crane, the extent of which may be de- termined by the length of the railway, and the bell may be brought to any part of the bottom which is perpen- dicularly below the parallelogram formed by the length of the railway.