The general solution of the equations connecting the motion of the two coupled components in an electromagnetic seismograph has been obtained in another paper and it shows that the magnification of a seismograph depend on seven instrumental constants. Using these results, equations and curves have been derived in the present paper from which the Magnification as well as Phase shifts in the response of a seismograph and their variations with damping and coil inductance can be easily obtained. Based on these curves a number of magnification curves for different combinations, which are in operation at the different seismological stations of the world, have been derived. Suitable equations and curves have also been obtained which can be used for estimating the absolute Magnification of a Seismograph. An experimental method of obtaining the frequency response curves of seismographs in their operating condition has been described and the results obtained by this method has been given. It has been indicated how the results incorporated in the present paper can be used in the proper design of seismographs required for the different purposes.

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The development of highly sensitive electromagnetic seismographs and their uses in various problems of seismology and other allied branches have considerably extended the region of their application. The theory of such seismographs was developed earlier under different approximations which are justified as long as it is used only in the study of earthquake waves of frequencies less than one cycle per sec. In the present paper the effect of large inductances in the transducer coils and also of any choke in the galvanometer circuit on the response characteristics has been examined. The response curves for different combinations of seismometers and galvanometers have been obtained, and their variations with the coil inductances have been estimated. It has been shown that considerable errors in the amplitude-period relationship occur if the coil inductances are neglected. This possibly explains the various anomalies which now exist in the interpretations of different results obtained from the analyses of seismograms, obtained with different seismographs. The ‘magnification curve’ for a typical electromagnetic seismograph has been obtained experimentally and this has been compared with the theoretical result derived in the present paper. A number of problems have been indicated, in the study of which precise response curves are required, and it has been suggested that with a proper use of the results derived here a large number of anomalies now existent may disappear.