-^■* 



Sect. VIL] 



EARTHQUAKE PHENOMENA, 



205 



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ment of the folded card, leaving the other free, and 

 thrust the whole into the horizontal limb of the tube 

 until the cork just touches the mercury, and so for the 

 others. This marker is shown at full mze (about) in 



Cork. 



Free side. 



Fig, 3. 



Attaclied side. 



The edges of the card having a certain amount of 

 elastic extension, must slightly grip the inside of the tube- 

 It will now be found that if horizontal motion be given 

 to the system of four tubes — say, from south to north, 

 that the marker in the southern tube will be pushed 

 southwards a certain space by the movement of the mer- 

 cury, and will remain to point out the space when the 

 mercury has returned to rest. If the motion be in some 

 direction between two adjacent tubes—say, from south- 

 east to north-west. — the markers in the south and e 

 tubes will both show a certain motion, equal in this case, 

 but in others with a certain ratio to each other, by which 





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the direction between the cardinal points may be cal 

 culated. 



For the vertical element : let the barometer- 

 tube Fiff. 4, be filled with mercury, so that about 

 six inches shall starid in the open end a^ into 

 which thrust a marker, as in Fiff. 3, and about 



F 



twelve inches in the sealed limb ; place this 



Fig. 4. 



vertically, and secure it to a fixed mass of rock, 

 a heavy low buildino;, or large tree ; the amount 

 to which the iHtarker is found moved up in the 

 tiihe will give the altitude of the wave ; and it 

 is obvious, that by the conjoint indications of 



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