and Recording Earthquake-Motions. 20i 



and carries two recording-levers, Z, V . The lever I is pivoted 

 at p and^/; and its action can be readily understood from the 

 figure. The lever V is crank-shaped, and is hinged to a cross 

 piece b, fixed to the front of the cylinder C and to the arm A 

 at p r This cross piece rotates as the cylinder rotates; and by 

 properly adjusting its length and the ratio of the arms of the 

 lever Z, the multiplication can be made the same as for /. A 

 drum carrying smoked paper (shown at D), or a circular glass 

 plate, may be revolved in front of the plate, and hence a record 

 of the different movements of the earth obtained. 



In this instrument the principle of neutral equilibrium can 

 be carried out to great perfection, as cylinders can be made 

 with great accuracy. It seems probable, from the preliminary 

 trials that have been made, that this arrangement may be 

 improved by allowing a smaller cylinder to roll freely inside the 

 large one. The advantage of this is the stability it gives, and 

 the quickness with which the cylinder comes to rest in its new 

 position after any motion. 



An interesting modification of this machine might be made 

 by placing two equal cylinders on a horizontal plate with 

 their axes parallel, and placing on them a second horizontal 

 plate so that its upper surface should always be in a plane 

 through their instantaneous axes. This could be done by causing 

 the plate to rest by means of arms on two pairs of smaller cylin- 

 ders of proper dimensions, so disposed that each of the larger 

 cylinders should bear at each end one of the smaller cylinders 

 coaxial w T ith the larger cylinder and projecting from it. A 

 third cylinder placed on the upper plate with its axis at right 

 angles to those of the first two would, for small motions of the 

 earth, have a line in itself which would remain approximately 

 at rest. Hence by proper registering-apparatus, perhaps 

 similar to that adopted for my rolling-sphere seismograph, a 

 record of the motion of the earth might be obtained. 



The instrument is shown in the diagram as arranged for the 

 registration of small motions ; but it is easy to modify this 

 arrangement so as to provide for the registration of motions 

 ranging in amplitude from a fraction of a millimetre to several 

 feet. All that is necessary is to arrange that, for very large 

 motions, the multiplying-lever shall go out of action, allowing 

 a direct-record arrangement to take its place. A very simple 

 method of writing large motions would be to attach a fine 

 point to the end of the cylinder at its centre, and allow this 

 point to write on a plate placed in front of it and fixed to the 

 base-plate P. For countries where the earthquake-motion is 

 measured in centimetres instead of in millimetres, as is the 

 case in Japan, an instrument of this form might prove of great 



