Download PDF, EPUB, Kindle A Text-Book of Geology Volume 1; Physical Geology

Download PDF, EPUB, Kindle A Text-Book of Geology Volume 1; Physical Geology

A Text-Book of Geology Volume 1; Physical Geology.cLouis Valentine Pirsson

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Author: Louis Valentine Pirsson
Page Count: 174 pages
Published Date: 01 May 2012
Publisher: Rarebooksclub.com
Publication Country: Miami Fl, United States
Language: English
ISBN: 9781236024091
File Name: A.Text-Book.of.Geology.Volume.1;.Physical.Geology.pdf
Download Link: A Text-Book of Geology Volume 1; Physical Geology
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 Excerpt: ...Seismographs.--Very delicate instruments have been invented, called seismographs, which record the tremors due to distant earthquakes, and the study of these records has led to important geological conclusions. The principle upon which such instruments are now constructed is simple; if a heavy mass of metal be suspended like a pendulum, owing to its inertia it will remain for a long time at rest when the shock arrives, while the earth vibrates beneath it. A point or pencil of some kind is secured to the suspended weight, while under it, on a bed-plate rigidly attached to the earth, is a paper or other medium suitably prepared to record the motions of the point which lightly touches it. If the earth oscillates beneath the suspended pencil a series of lines will Fig-196 be drawn on the vibrating paper. If the paper, instead of being made fast, be a strip continuously carried along by clockwork the pencil when at rest will draw a straight line upon it; when vibrations of the earth occur the line will be broken and will oscillate sinuously from one side to the other. See Fig. 197. Such a record is known as a seismogram. While in principle, a modern seismograph is simple, in construction it is a rather complicated instrument (see Fig. 196) since it is arranged to record not Seismograph with astatic pendulum, Wiechert's model. only horizontal motion in two directions, East-West and North-South, but also the vertical motion as well. It is from such records in three directions that the wire models shown on page 247 are constructed. Since the intervals of time are marked on the moving paper, the instrument records the time of arrival of the shock and also the duration. The directions of diversion of the markers from their regular paths show also the direction from w...

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