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| Keywords: The Quarterly journal of the Geological Society of London (13204645565).jpg 220 <br> T GRAY Otf A SEISMOGRAPHIC APPARATUS <br> or vertically The pendulum P is kept deflected by means of a light <br> brass tube which passes through its centre in a direction at right <br> angles to its axis and which carries at one end a vertical knife-edge <br> and at the other end a very light index of aluminium foil This <br> thin tube rests Avith its knife-edge in a flat Y-groove which is fixed <br> to the supporting column C ; and by sliding it more or less through <br> the tube a greater or less deflection can be given to the pendulum <br> The other pendulum is exactly similar to P with the exception that <br> the aluminium index is fixed at right angles to the tube and close to <br> the knife-edge By this arrangement the two pointers can be ad- <br> justed to lie in the same horizontal plane and in parallel directions <br> When so adjusted the planes of deflection of the pendulums are at <br> right angles to each other The point of suspension is adjusted to <br> be a little in front of but very nearly vertically above the knife- <br> edge so that the period of free vibration of the pendulum round a <br> vertical axis is long compared with the period of vibration of the <br> earth The vertical component is recorded by means of a compen- <br> sated spring seismograph see Phil Mag Sept 1881 which consists <br> of a mass M figs 1 3 attached near one end of a horizontal lever I <br> Fig 3 ” Diagram of Spring -Seismograph recording vertical <br> movements <br> which turns freely round a knife-edge at and is supported by the <br> flat springs S which are attached to the lever by links working on <br> knife-edges To the free end of the lever one end of a small box 36928817 113681 51125 Page 220 Text 39 http //www biodiversitylibrary org/page/36928817 1883 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 39 1883 Geology Periodicals Smithsonian Libraries bhl page 36928817 dc identifier http //biodiversitylibrary org/page/36928817 smithsonian libraries Information field Flickr posted date ISOdate 2014-03-16 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/13204645565 2015-08-26 13 56 42 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1883 Photos uploaded from Flickr by Fæ using a script | ||||
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