EARTHQUAKES AND OTHER SEISMIC MOVEMENTS. 307 



dragon-heads, each of which holds a ball in its mouth. Underneath 

 these heads there are eight frogs so placed that they appear to watch 

 the dragon's face, so that they are ready to receive the ball if it should 

 be dropped. All the arrangements which cause the pillar to knock 

 the ball out of the dragon's mouth are well hidden in the bottle. 

 When an earthquake occurs, and the bottle is shaken, the dragon in- 

 stantly drops the ball and the frog which receives it vibrates vigor- 

 ously. Any one watching this instrument can easily observe earth- 

 quakes. With this arrangement, although one dragon may drop a 

 ball, it is not necessary for the other seven dragons to drop their balls 

 unless the movement has been in all directions : thus we can easily 

 tell the direction of an earthquake. Once upon a time a dragon 

 dropped its ball without any earthquake being observed, and the peo- 

 ple therefore thought the instrument of no use, but after two or three 

 days a notice came, saying that an earthquake' had taken place at 

 Rdsei. Hearing of this, those who doubted the use of this instrument 

 began to believe in it again. After this ingenious instrument had 

 been invented by Choko, the Chinese Government wisely appointed a 

 secretary to make observations on earthquakes." This, the most an- 

 cient of the whole class, is closely resembled by some of the instru- 

 ments of modern times. 



The Japanese have an instrument consisting of a magnet holding 

 up a nail, which, when shaken off, starts the train of an alarum, but this 

 does not seem to have ever acted with success. Other seismoscopes 

 depend upon the overthrow of a round column of wood or metal, the 

 projection of balls which are connected with electric circuits, or the 

 disturbance of liquids. Some seismographs depend upon the motions 

 of a pendulum, which may be made to show whether the direction of 

 the shock has been constant or variable, and the maximum extent of 

 its motion in various directions. Other instruments are formed by 

 various adjustments of movable bodies, or with springs and adapta- 

 tions of clock-work. For a complete seismograph we require three 

 distinct sets of apparatus an apparatus to record horizontal motion, 

 one to record vertical motion, and one to record time. These princi- 

 ples are all embodied in the Gray and Milne seismograph, which is now 

 in use in Japan. In this apparatus (Fig. 2) two mutually rectangular 

 components 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 motion is recorded on the same sheet of 

 paper by means of a compensated-spring seismograph, S. L. M. B. 

 The time of occurrence of an earthquake is determined by causing the 

 circuit of two electro-magnets to be closed by the shaking. One of 

 these magnets relieves a mechanism, forming part of a time-keeper, 

 which causes the dial of the time-piece to come suddenly forward on 

 the hands and then move back to its original position. The hands are. 



