390 E. F. PIGOT. 



being carried on during the last few years according to more 

 rigorous scientific methods. And if also, quite apart from 

 their registration of earthquake movements properly so 

 called, the instruments, used as clinographs rather than 

 seismographs, might possibly in the course of years, reveal 

 slow progressive tilting, the ascertained direction of which 

 would throw some light on the nature of any geotectonic 

 movement of the Australian Cordillera and the bed of the 

 western Pacific, they would, I think, have an additional 

 usefulness. I eventually decided to commence with the 

 two instruments I am about to describe, which were erected 

 in February last, immediately on their arrival from Ger- 

 many, in the seismograph-cellar specially built for them in 

 a secluded spot in the college grounds, far from any artificial 

 source of vibration or disturbance. Both of these seismo- 

 meters are designed by Professor Wiechert, of the Geo- 

 physical Institute (and University) of Gottingen, one of 

 them registering the two components (N.S. and E.W.) of 

 the horizontal movement, the other the vertical component, 

 of the earth-waves. 



And first, as regards the horizontal seismograph. It is 

 fully described in Professor Wiechert's original paper, 

 published in the " Physikalische Zeitschrift," 4th year, 

 No. 28, pp. 821 and seq. 1 He calls it an " astatic pendulum 

 of high sensibility for the mechanical registration of earth- 

 quakes." He adopted a mode of suspension differing com- 

 pletely from those in general use. While the Italian school 

 of seismology, as represented by the instruments of Pro- 

 fessors Vicentini and Agamennone, has favoured mainly, 

 though not exclusively, the "vertical" type of pendulum, 

 a heavy bob (the so-called " steady-mass," "dead mass," 

 or "stationary-mass") suspended by stout wire, the non- 



1 A detailed account of it is also to be found in the "Annuaire. Astro- 

 nomique " for 1907, published by the Royal Observatory of Belgium, p. 

 470 and seq. 



