TIMES OF YAKUTAT BAY EARTHQUAKES 391 



A comparison of these three sets of records shows a close agreement in 

 two out of the three. In the case of the heavy final shock of September 

 10 the agreement is within 43 seconds, and in the case of the September 

 3d shock the determinations check within 70 seconds, coming very close 

 to the possible error of ^^one minute of time" which Doctor Oldham 

 allows himself (page 386). So close a determination must be a source 

 of gratification to Doctor Oldham, as this was probably the first attempt 

 ever made to determine times of origin from distant seismograph records. 



The agreement of the two sets of records also accords well with the 

 assumption that the chief shocks on September 3, September 10 and 

 23 had their principal origins in or near Yakutat Bay. It should be 

 remembered, however, that the rate of transmission assumed, 3 kilometers 

 per second, on which the local time records are based, is wholly arbitrary. 

 The most recent studies of velocity of propagation suggest that a rate of 

 7 or 8 kilometers per second may have been attained. 



SPEED OF TRANSMISSION 



An attempt to check the determination of rate of transmission by 

 comparison with the only other local time records of any accuracy. Pro- 

 fessor Gwillim's observation near Atlin on September 10, a place almost 

 exactly as far east of Disenchantment Bay as Cape Whitshed is west of 

 there, and Judge Myers' observation at Eagle, about 340 miles north- 

 northwest of Disenchantment Bay, results as follows : 



Time of observation, 12h. 45m. Os. p. m., local solar time near Atlin; 

 latitude of place of observation, near Atlin, 59° 24' 30" north; longitude, 

 133° 35' 0" west; latitude of Disenchantment Bay, 59° 58' 20" north; 

 longitude, 139° 33' 0" west). Correcting this observation for a differ- 

 ence of 23 minutes and 52 seconds of time with 5° 58' of longitude, we 

 find that the shock appears to have been felt by Professor Gwillim at 

 12h. 21m. 8s. (Yakutat Bay time), or 53 seconds before it originated at 

 Yakutat. 



Similarly a correction of the supposed accurate local solar time obser- 

 vation at Eagle (latitude 64° 13' north; longitude 141° 15' west), where 

 the earthquake was felt in the Weather Bureau observatory at 12h. 15m. 

 p. m., results as follows: A correction of 6m. 48s. of time for 1° 42' of 

 longitude shows that the shock was felt by Judge Myers at 12h. 21m. 48s. 

 (Yakutat Bay time), or apparently 13 seconds before it was generated at 

 Yakutat. 



It might be either that (a) the time of origin given by us for Yakutat 

 Bay is a minute, more or less, too late, as it would be if we assumed too 

 fast a rate of transmission from Yakutat to the Coast Survey camp at 



