48 THE ROYAL SOCIETY OF CANADA 



from the seismogram knowing at the same time that it is a question- 

 able procedure. 



The above sections or periods were each enlarged photographic- 

 ally to the required 400 mm. The harmonic analyzer is adapted for 

 thirty components, that is, the analysis of a periodic wave will show 

 which of the simple thirty sine waves are concerned and to what degree, 

 as shown by the amplitudes, in producing the periodic wave. 



The thirty components represent those waves whose periods are 

 respectively the quotient of the period of the composite wave divided 

 by the respective component; the 30th component will have a period 

 half as long as the 15th, or a third of that of the 10th, and so on. 



The analyzer takes five components at a time, so that, for the 

 thirty, six tracings or followings with the stylus of the gram of 400 mm. 

 are necessary. 



The accuracy of the constants obtained and read off from the 

 analyzer is readily shown by inserting them in the synthesizer — 

 turning a handle — when the compound curve is traced on a sheet of 

 paper, — in our case scarcely distinguishable from the original seismo- 

 gram. 



The seismograms are from a Bosch photographic seismograph 

 having two components, the N-S one having air-damping, while the 

 E-W one has magnetic damping by means of a strong horse-shoe 

 wolfram-steel magnet, the horizontal pendulum rod being extended 

 by a light aluminium plate moving between the jaws of the magnet, 

 so that the magnetic damping renders the horizontal pendulum 

 almost aperiodic. 



The results of the analysis are given in the subjoined table: 



