October 27, 1922] 



SCIENCE 



479 



homogeneous medium; that is, homogeneous as 

 to stress effects or, in other words, isotropic. 

 The resultant vibrations which travel circum- 

 ferentially from the shock center pass through 

 what we know is a heterogeneous medium." 

 Rudzki^ has shown that a disturbance in a 

 heterogeneous but stratified elastic solid will 

 send out distinct types of waves. These waves 

 will be propagated through the stratified me- 

 dium at different velocities and will appear in 

 separate groups. First a nearly longitudinal 

 phase will arrive at a given point, then a 

 double, approximately transverse phase, and 

 finally a group of surface waves will travel on 

 the free surface. 



But when the author of the article goes on 

 to say: "The wave types are not separated in 

 the earth's surficial shell. At a minimimi dis- 

 tance of 700 miles, or 10 degrees of arc, from 

 the epicenter a three-phase record becomes de- 

 cipherable," he is unfortunately allowing him- 

 self to be betrayed into statements at variance 

 with a great and ever-increasing mass of ob- 

 served and published facts. The reports of 

 any of the better seismographic stations, 

 equipped with modern damped apparatus, 

 would have furnished him with examples to the 

 contrary. So, too, would any of the bulletins 

 that are being issued by the Seismological 

 Committee of the British Association*, or 

 Angenheister's^ recent study on Pacific earth- 

 quakes and the ujjper layers of the earth's 

 crust. The Chittenden,^ California, earthquake 



3 M. P. Rudzki : 1. " Parametriselie Darstellung 

 der elastischen Welle in anistropen Medien, ' ' 

 Bull. Acad. d. Sciences de Cracovie, 1911, pp. 

 503-536. 



2. ' ' Sur la propagation d 'una onde elastique 

 superfieielle dans un milieu transversalement iso- 

 trope," lUd., 1912, pp. 47-58. 



■i" The -Large Earthquakes of 1917," Oxford, 

 1921. 



^ G. Angenheister: " Beobaelitungen an pazi- 

 fischen Beben. Ein Beitrag ziim Studium der 

 obersteu Erdkruste, " Nachr. d. Ges. d. Wiss. zu 

 Gottingen, Math.-Phys. Kl., 1921. 



f Located at Chittenden, Santa Cruz Co., Cal., 

 by Wm. J. Kemnitzer. See: William J. Kemnit- 

 zer, ' ' The Chittenden Earthquake of July 24, 

 1921," Bull. Seism. Soc. Am., Vol. XI, pp. 189- 

 191, September-December, 1921. 



of July 24, 1921, was an unusually beautiful 

 example of clean-cut separation of the three 

 phases at very short distances. As published 

 in the Bulletin^ of the Seismographic Stations 

 of the University of Cailifornia, the epicentral 

 distance obtained from the Berkeley seismo- 

 grams was only 125 km. (78 mi.) and that 

 measured on the Lick records was but 46 km. 

 (29 mi.), both of which agree very well with 

 the location of the epicenter at Chittenden on 

 macroseismic evidence. 



There is another argument in the paper that 

 is open to controversy. Belying on the state- 

 ments of Professors Knott and Oldham that 

 compression waves are transmitted through the 

 core of the earth while shear waves are not, the 

 author argues .to a viscous fluid state of the 

 interior. Now it is by no means certain that 

 the transverse waves do not pass through the 

 core of the earth. Neither, on the other hand, 

 is it an observed fact that the longitudinal 

 waves do so penetrate. In fact, the evidence 

 seems rather strong to the contrary. Weiehert 

 and Zoeppvitz,^ Zeissig° and Mohorovicic"^" 

 were not able to trace the direct longitudinal 

 waves much more than half way to the 

 antipodes. Gutenberg^'- in 1914 followed them 

 up to about 106° and thought he had evidence 

 for their reappearance between 143° and 180°. 



" James B. Macelwane : ' ' The Eegistration of 

 Earthquakes at the Berkeley Station and at the 

 Liek Observatory Station, April-September, 

 1921," U7iiv. of California PuM., Bull, of the 

 Seism. Stat., Vol. 2, No. 2, 1922. 



s E. Wiechert und K. Zoeppritz : ' ' tJber Erd- 

 bebenwellen I u. II, ' ' Nachr. d. K. Ges. Wiss. zu 

 Gottingen, Math.-Phys. Kl, 1907. 



OK. Zeissig: "Tabelle," Akad. Nauk, St. Pe- 

 tersburg, Comptes rendus des seances de la Com- 

 mission sismique permanente. Tome III, Liv. III. 



1° S. Mohorovicic : ' ' Die reduzierte Lauf zeit- 

 kurve. II. Mitteilung: Die Ausbreitung der Erd- 

 bebeustrahlen in den tiefen Schichten der Erde, " 

 Gerlands Beitrdge zur Geophysilc, Bd. XIV, Heft 

 3, 1916. 



11 B. Gutenberg: "tJber Erdbebeuwellen VII 

 A. Beobaehtungen an Eegistrierungen von Fern- 

 beben in Gottingen und Folgerungen iiber die 

 Konstitution des Erdkorpers (mit Tafel)," A''ac7ir. 

 d. K. Ges. d. Wiss. zu Gott., Math.-Phys. Kl., 

 1914. 



