COMPARISON OF EARTHQUAKE DIAGRAMS. 67 



leading to the same result which shows that the particles of the earth 

 move in space in a most irregular and complex manner, and to try to 

 picture the path pursued at the time of an earthquake is almost a 

 hopeless task. 



The ratio of the principal vertical to the horizontal movement 

 ranges from 1 to 7 to 1 to 3 for amplitude, 1 to 2 for average period, 

 and 1 to 2.4 for duration of disturbance. 



Conclusions regarding the agreement of two diagrams of 

 Horizontal Motion given by the same earthquake. 



The object of the present paper is not so much to discuss the 

 character of earthquake motion as to examine the agreement of two 

 diagrams of the same earthquake taken by two Horizontal Pendulum 

 Seismographs. If we go right through the records, wave by wave, 

 or by means of the successive short radial lines, we will notice (taking 

 into account the multiplying ratio of Plates YIII. and X. to be four 

 and that of IX. and XL to be nearly six) that the corresponding 

 pointers in the two seismographs produced waves of exactly the same 

 amplitude and period, both marking even irregular minor ripples 

 between the principal undulations. These coincidences are faithfully 

 repeated through all changes of amplitudes and periods to the end 

 of the disturbance. 



Such coincidence means either of two things, — (l)the steady mass 

 in the instrument which serves as a datum line for registering earth- 

 quake motion remained stationary; or (2) the said mass in each instru- 

 ment was moved exactly in the same manner during the prolonged 

 shaking, and produced exactly the same error throughout. But what 

 is called the steady mass is a hanging bob suspended by a horizontal 

 lever, and therefore is free to oscillate round the axis of support with 

 its own period of five to six seconds, or in other words, the bob 



