470 Analysis of Alicroseismograms. 



sets of waves gave rise to maxima at average intervals of one 

 minute, and this feature is clearly shown on the records. 



10. Another interpretation, however, is that the analysis 

 employed has effected a separation of the observed movement 

 into more than two simple harmonic components, for we may 

 write 



22 sin (6°*- 12°) sin 120°'2t-t-20 sin (5° t-70°) 



sin(134°-5£ + 56°) 

 in the form 



11 cos (114°-2 t - 12°) - 11 cos (126°-2 £-12°), 



+ 10 cos (129°-5 t- 126°) - 10 cos (139°-5 t - 14°) . 



In view of the uncertainty attaching to the values found 

 for the speeds, the terms 



10 cos (129°-5 * — 126°) and 11 cos (126°'2 t-12°) 



are hardly distinguishable one from the other, and there is a 

 possibility that the number of component harmonics is only 

 three, with speeds about 114°, 127°, and 139°. 



The smallness of the amplitudes makes a closer determi- 

 nation of the angles impossible. It is therefore desirable to 

 see whether other portions of the sei sinogram confirm the 

 result just obtained. The portion of the trace analysed 

 formed part of the fifth line of Plate 7 A. and portions of the 

 traces in the first, second,. third, seventh, and eighth lines 

 were measured and treated in the same manner. 



As a rule, the equations of conditions were well satisfied 

 by the assumption of the existence of two periodic terms, 

 but in two cases somewhat smaller residuals were obtained 

 by the assumption that three terms were involved. 



The values of the speed angles thus found are here tabu- 

 lated. 



Line 1. 1st solution l29°o, 114°-1 



2nd solution 131°'6, 119°-8 



Line 2. Assume two periods 134°"2, 115° - 4 



Assume three periods 134°"9, 122°-4, 82°-2. 



Line 3. Assume two periods 148°'7, 125°\5 



Assume three periods 149°'5, 120° 2, 45°-5. 



Line 5. Assume two periods 134°o, 120 o, 2 



Since, however, the amplitudes vary, it is more correct 

 to say that there are three 

 periods whose speed values are 139°, 127°, 114°. 



Line 7 129°-6, 112°-2 



Line 8 140 o> 9, 110° 



