. Earthquakes and other earth movements. Earthquakes. 32 EAKTHQUAKES. from such instruments, chiefly on account of the incon- venience in making a spring sufficiently long to allow of enough elongation to give a long period of vibration. Similar remarks may be applied to the horizontally placed elastic rods, one end of which is fixed to a wall, whilst the opposite end is loaded with a weight. Such contrivances, furnished with pencil on the weight to write a record upon a vertical surface, were used in 1842 at Comrie, and we see the same principle applied in a portion of Palmieri's apparatus. C
. Earthquakes and other earth movements. Earthquakes. 32 EAKTHQUAKES. from such instruments, chiefly on account of the incon- venience in making a spring sufficiently long to allow of enough elongation to give a long period of vibration. Similar remarks may be applied to the horizontally placed elastic rods, one end of which is fixed to a wall, whilst the opposite end is loaded with a weight. Such contrivances, furnished with pencil on the weight to write a record upon a vertical surface, were used in 1842 at Comrie, and we see the same principle applied in a portion of Palmieri's apparatus. Contrivances like these neither give us the true amplitude of the vertical mo- tion, insomuch as they are readily set in a state of oscil- lation ; nor do they indicate the duration of a disturbance, for, being once set in motion, they continue that motion in virtue of their inertia long after the actual earthquake has ceased. They can only be regarded as seismoscopes. The most satisfactory in- strument which has yet been devised for recording vertical motion is Gray's horizontal- lever spring seismograph. This instrument will be better understood from the accompanying sketch. A vertical spring s is fixed at its upper end by means of a nut n, which rests on the top of the frame F, and serves to raise or lower the spring through a short distance as a last adjustment for. Fig. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Milne, John, 1850-1913. New York, D. Appleton and company
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