長週期地震計の製作(第2報)

抄録

In the first paper (This Jour. Vol. 14, No.8) we have described about the long-period seismograph of mechanical registeration with a device of electric amplifying. This instrument was made so as to be usable for the routine work of seismological observation. At present it was installed at the Kôbe Meteorological Observatory.
The principle of the instrument now presented is the same as that used in the former case, but some new devices and improvments are made, especially in the part of generating electric current and recording galvanometer circuit. The magnification curve of this instrument for earthquake movements of various periods is obtained and shown in Fig. 4. It varies according to the state of adjustment of amplifier and three curves shown in Fig. 4 are examples in certain states in certain states usually used in actual observations.
The curve is very alike to that obtained for Galitzin's seismograph of photographic resisteration. But this instrument has an advantage according to the smallness of the period of recording galvanometer and moreover the magnification can be made very large, probably it will attain for more than 10, 000 if desired for earthquake of a small periods and this is easily done by diminishing the capacity of condensers put in some parts of amplifier.
But our present aim does not lie there. For earthquake of ordinary distance the magnification becomes to be about 1, 000 or more.
At any rate the writers consider that for the observation of any kind of earthquakes, especially for distant earthquakes, this instrument must play an important rôle. Some examples of seismograms obtained by this instrument are shown in Plate 8, with those of the same earthquakes obtained by Wiechert's 200kg seismograph (V=80) given as a reference. By these seismograms we can clearly see how powerful is our seismograph with electric magnification for the observation of distant earthquakes compared with the mechancally resistering seismographs ordinarilly used.