EARTHQUAKES. 



303 



which will swing according to the intensity 

 and direction of the shock, or a ball balanced 



11 

 P 







CHINESE SEISMOMETER. 



in such a way that any tremor of the earth 

 will cause it to roll a proportionate distance. 

 The most ancient seismometer known, is one 

 in China. Its general appearance will be ap- 

 arent from the accompanying illustration. 

 t was invented about 136 A. D., by a Chi- 

 ese called Choko. Its outer appearance is 

 shown by the engraving. In the 

 inuer part a column is suspended 

 so that it can move in eight di- 

 rections, and there is also an ar- 

 rangement by which some record 

 of the earthquake is made by the 

 moving column. On the outside 

 are eight dragons' heads, each of 

 which holds a ball in its mouth. 

 Underneath these heads are eight 

 froars, placed with open mouths 

 ready to receive the ball if it 

 should be dropped or knocked 

 out by the move- 

 ment of the col- 

 umn. When the 

 earthquake occurs, 

 and the instrument 

 is shaken, a dragon 

 instantly drops a 

 ball, and the frog 

 that receives it vi- 

 brates vig- 

 orously. Al- 

 though one 

 dragon may 

 drop a ball, 

 it is not ne- 

 cessary for 

 the other 

 seven drag- 



GRAY AND MILNE'S SEISMOGRAPH. 



ons to drop their balls, unless the movement 

 has been in all directions. Thus the direc- 

 tion of the earthquake is shown. The diame- 

 ter of this instrument is eight feet. Not 

 only is this instrument of interest because of 

 its antiquity, but also because on account of 

 the close resemblance that many modern in- 

 struments bear to it. Another instrument, 

 also of Eastern origin, is the magnetic seis- 

 moscope of Japan. On the night of the de- 

 structive earthquake of 1855, which devas- 

 tated a great portion of Tokio, the owner of 

 a spectacle-shop in Asakusa observed that a 

 magnet dropped some old iron nails and keys, 

 which had been attached to it. From this oc- 

 currence the owner thought the magnet had, 

 in consequence of its age, lost its powers. 

 About two hours afterward, however, the 

 great earthquake took place, after which the 

 magnet was observed to have regained its 

 power. The latest and most complete appa- 

 ratus is the seismograph, invented by Messrs. 

 Gray and Milne ; it records the horizontal mo- 

 tion, the vertical motion, and the time. Mr. 

 Milne thus describes it : 



In this apparatus two mutually rectangular com- 

 ponents of the horizontal motion of the earth are 

 recorded on a sheet of smoked paper wound round 

 a drum, D, kept continuously in motion by clock- 

 work, W, by means of two 

 conical pendulum - seismo- 

 graphs, C. The vertical mo- 

 tion is recorded on the same 

 sheet of paper by means of a 

 compensated - spVing seismo- 

 graph, S, I, M, B. The time 

 of occurrence of an earth- 

 guake is determined by caus- 

 ing the circuit of two electro- 

 magnets to be closed by the 

 shaldng. One of these mag- 

 nets relieves a mechanism, 

 forming part of a time-keeper, 

 which causes the dial of the 

 timepiece to come suddenly 

 forward on the hands and 

 then move back to its original 

 position. The hands are pro- 

 vided with ink-pads, which 

 mark their positions on the 

 dial, thus indicating the hour, 

 minute, and second when the 

 circuit was closed. The sec- 

 ond electro-magnet causes a 

 pointer to make a mark on 

 the paper receiving the record 

 of the motion. This mark 

 indicates the part of the earth- 

 quake at which the circuit was 

 closed. The duration of the 

 earthquake is estimated from 

 the length of the record on 

 the smoked paper and the 

 rate of motion 

 of the drum. 

 The nature 

 and period of 

 the different 

 movements 

 are obtained 

 from the 

 curves drawn 

 on the paper. 

 Mr. Gray has 



