The spectrum of seismic waves has recently become a matter of increasing interest to seismologists and structural engineers. In view of the trouble of numerical harmonic analysis without instrumental means, other simpler means of approach to this problem have been frequently sought, among which must be mentioned the frequency curve of different periods examined by many investigators. Of late years, however, electric analog computers and other instruments for this purpose have been introduced and used conveniently. But so far as the writer is aware, the basic principles of these vibration analysers are not yet solved completely. He therefore presents some notes on this subject.最近振動の解析が理工学の各分野に於て盛んに行われるようになり,その為に簡便な共振系が利用されているが,その理論に就いては必ずしも明かにされて居ない点がある.次にその2~3に就いて述べる