122 F. OMORi : 



been given by Ewing\ Davison^, Hecker^ Pacher* and others. 

 But witli regard to the registration, it must be pointed out that 

 there are two methods of doing this, photographic and mechanical, 

 of which the latter, so far as the observation of earthquakes 

 and similar earth movements is concerned, seems to be the best. 

 Thus, for instance, the Horizontal Pendulum Apparatus of 

 Paschwitz is well adapted for observing the level change of the 

 ground, but, when seismometrically used, it is merely a species 

 of very delicate seismoscope, unless the rate of motion of the 

 photographic paper is very rapid. For, with such a small rate 

 of motion of the paper as was adopted by Paschwitz, about 2 cm. 

 per hour, the photogram shows only the extent of motion of the 

 light point, and tells nothing about the period of vibration of the 

 earthquake motion. In fact it is, I think, a great mistake to take the 

 range of motion in such photograms as the representative, or direct 

 result, of any tilting motion of the ground : firstly, because, in 

 an earthquake, the horizontal pendulum of Paschwitz is usually 

 thrown into its proper oscillations of considerable amplitude, 

 and, secondly because the earthquake movements registered by 

 such pendulums are probably due to the horizontal motion, and 

 not to the tilting of the ground. (See §§16,26). With a quick 

 rate of motion of about 30 cm. per hour of a very sensitive 

 photographic paper, we can obtain open earthquake diagrams 

 clearly showing individual movements of the pendulum, as 

 well as the " pulsatory oscillations " or small earth movements 



1. J. A. Eiving. Earthquake Measurement. Memoirs of the Science Department, 'Tokio 

 Daigaku, No. 9. 188."5. 



2. C. Davison. The Horizontal penduhim. J^atural Science Vol. VIIL 50. April, 1896. 



3. 0. Hecker. Das Horizontalpendel. Zeitschrift fur Imlrumentenkunch, 1896, Januar. 



4. Giidio Packer. I Microsismografi dell'Istituto di Fisica della R. Università di 

 Padova. Atti del B. htituto Veneto di Scienze, etc. Tomo VIII, Serie VII.—189&-97. 



