268 T- "TfiRADA and T. Matuzawa 



II. Instrumental Investigations. 



(a) Instruments. The invaluable services of Omori's horizontal 

 l)enduluin and tromometer^^^ which have been rendered for the develop- 

 ment of seismolog'y in this country need no special comment. Among 

 tlie other instruments, Imamura's form^'^ with two-fold magnification 

 has proved excellent I'or recording near earthquakes and was the only 

 instrument which furnished us with the most precious r, cord of 

 the recent great earthquake which put all other instruments out of 

 action. 



The introduction of a damper on Omori's instrument has also 

 been contemplated in this country. Saem. Nakamura's modification^^^ 

 with a special dami)ing device and other points of improvement has 

 been in actual use in some quarters. He later^"*^ made some discus- 

 sions on the theory of vertical seismometer. 



Tamaru's vertical seismograp¥'^^ with two springs for suspension 

 is devised to avoid the instability due to the third power of the 

 angle of deviation appearing in the expression of the pot(.utial energy 

 of the system. With successive improvements at different points, the 

 instrument is now in actual use in a number of observatories. Tamaru 

 also elaborated the design of a new seismograph which is intended 

 to record the two or three components of acceleration, by using a 

 single suspended weight. A model is now under construction and 

 being tested under his supervision. 



Omori"'^ devised also an improved form of horizontal pendulum 

 by introducing the principle of the duplex pendulum. Tanakadate"^^^ 

 constructed a strong earthquake recorder by making use of Watt's 

 parallel motion arrangement. A form of vertical seismograi)h is also 

 due to him which was later utilized by S. Yokota for recording the 

 vibrations of ships. 



(1) Ho., 50 (1905); Pub., 12 (1903); 18 (1904); Bull., 1, No. 4 (1907) ; T.S.B.K., 

 1 (1902), 143; Journ. Coll. Sci. Tok., 11 (1899), 121. 



(2) J.M.S., 31 (1912), 171. 



(3) J.M.S., 39 (1920), 1. See also K. Hasegawa, J.M.S., 31 (1912), 297 ; K. Siida, 

 Umi to Sora, 2 (1922), 2, 38 aud 65. 



(4) T.S.B.K., [iii] 3 (1921), 101. 



(5) J.M.S., 30 (1911) special pages in Ho/iiazi; 37 (1918) same; see also Hasegawa, 

 J.M.S. 33 (1914), 239. 



(6; T.S.B.K., 2 (1904), 118. 

 (7) Pub., 7 (1902). 



