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Symposium on Microseisms 



target but should be encouraged to find the 

 reasons for his misses. 



When Sir Isaac Newton first measured the 

 velocity of sound in air by measuring the pres- 

 sure and density, he obtained a value ridicu- 

 lously far from the accepted value. He 

 erroneously attributed his erratic result to the 

 fact that air is not a perfect gas. Since no 

 actual gases are perfect gases, he should, fol- 

 lowing Dr. van Straten's logic have given up 

 the method since it would fail in more cases 

 than it would succeed. Fortunately for Phy- 

 sics, further investigations were conducted. 

 These finally led LaPlace to point out that not 

 the method but Newton's explanation of his 

 failure was incorrect. This may well be true 

 in Gilmore's case. Newton's erratic result 

 arose from his treating sound as an isothermal 

 process whereas actually it is an adiabatic pro- 

 cess. With this correction the method has been 

 used successfully to measure the velocity of 

 sound in all gases. The analogy is far from 

 perfect but applying the same reasoning here, 

 I would disagree with Dr. van Straten's criti- 



cism of Gilmore's work "that it does not permit 

 a decision one way or another" and say rather 

 that since it has proved successful in some 

 cases, it represents progress and should be con- 

 tinued until the reason for its failure in other 

 cases is definitely established beyond question. 



As the second proponent of the storm 

 center theory, the work of the Lamont Observa- 

 tory is cited — presumably the work of Wm. 

 L. Donn. Since Donn's work differs from Gil- 

 more's chiefly in that Donn assigns a definite 

 theory of the origin of microseisms, I shall pass 

 over this section of Dr. van Straten's paper. I 

 should like to mention however that it is un- 

 fortunate that Ramirez, Gilmore and Donn all 

 used average values of time intervals in deter- 

 mining the direction of the microseismic source. 

 It would have been more satisfying if direction 

 had been obtained from time intervals of indivi- 

 dual waves. The resulting directions could 

 then be grouped into the most prominent ones 

 and the presence of more than one seismic 

 source would at once become apparent. 



1951 NOV. 25,Oh. DEC. I, Oh. 



DEC. 17, Oh. 



1952 JAN. 2, Oh. 



Figure 1. (A) Amplitudes of regular microseisms with periods of 5-8 seconds recorded at Santa 

 Clara University, California, during November-December, 1951, and highest recorded 

 ocean waves at Ellwood, California. ( B) Periods of microseisms at Santa Clara and 

 periods of ocean waves recorded at Ellwood and at Camp Pendleton, California. 



