392 



E. F. PIGOT. 



which axis is connected the equilibrating steel spring 

 referred to above ; the point D will therefore repeat on a 

 large scale the movements of A, in the direction A B. D 

 is connected on one side to the piston of the damping- 

 cylinder H", by means of which the pendulum is rendered 

 almost aperiodic or u dead-beat " (a point of vital import- 

 ance now universally recognized, and first insisted upon 

 and introduced into instrumental seismology by Professor 

 Wiechert), and on the other by means of the rod D E with 

 the arm E F and the vertical axis F G: the oscillations of 

 D are thus communicated in a highly magnified form to the 

 platinum stylus writing on smoked paper at the extremity 

 of the arm Q. 



In fig. 2, another rough 

 diagram, is illustrated 

 the action of the vertical 

 seismometer, the letters 

 indicating the same 

 parts as in the above. 

 The "stationary-mass" 

 M in this case weighs 

 80 kilograms and is 

 attached to one end of a 

 lever O M whose fulcrum is at O, the weight of M being 

 antagonised by a helical steel spring R, applied at the point 

 P. Thus the vertical component of the earth-movement 

 in an earthquake will affect and alter the equilibrium-position 

 of O M, which will oscillate in a vertical plane, the oscilla- 

 tions being communicated by the arm O A and rod A B to 

 the lever D D', moveable about C in a horizontal plane. 

 The ends of this lever, D and D\ are connected in a manner 

 quite similar to that already described for the horizontal 

 components, and transmit the movement on the one hand 

 to the damping-piston at If, and on the other to the record- 



