Öiä S. SEKIYA. 



It is tlie writer's intention to give, in the next number of this 

 Journal, the general results of observations especially relating to 

 Vertical Motion and therefore the record ofthat motion is here studied, 

 as a preliminary, in conjunction with horizontal movement. It is only 

 by compounding the vertical and horizontal motions that we can 

 obtain the complete tracing of the motion of the earth particles during 

 an earthquake. 



PLATE VIII. AND PLATE IX. 



The Earthquake of Maij .18th, 1886. — This earthquake disturbed 

 the plain of Musashi and its neighbouring provinces including a 

 radius of 85 miles around ; the origin of disturbance was inland 32 

 miles N.N.AV. from the Observatory, It did scarcely any damage to 

 buildings. 



Instrument?. — The record of the earthquake is shown by Plate 

 VIII, which Avas taken by Prof. J. A, Ewing's Horizontal Pendulum 

 Seismograph ; the waves on the inner circle were traced by a pointer 

 which registered north to south components of motion, and those on 

 the outer circle by another which registered east to west motion. The 

 pointers tracing these components are prolongations of horizontal 

 pendulums, which magnify the motion of the ground four times, and 

 produce their records on a revolving glass plate which is started by 

 means of an electric contact maker. The plate is driven by a clock- 

 work train, which, after starting, quickly reaches a steady rate under 

 the control of a friction governor. The speed of rotation was one 

 revolution in 80 seconds; the short radial lines mark seconds, so that 

 the successive movement of the earth may be studied in conjunction 

 with time. 



Plate IX. which is the I'ecord of the same earthquake as that of 

 Phite A^III. has the record of both horizontal and vertical motions ; 



