EARTHQUAKES—BULLEN 331 
few observatories recorded the waves, the results are seismically valu- 
able, and have supplied important corrections to the travel-time tables. 
From 1947 until 1957 there was no general release of source data 
on nuclear explosions in any country, although in some cases individual 
seismologists have been given access to data. For example, Dr. B. 
Gutenberg and Dr. D. S. Carder have been able to make important 
inferences from records of a number of explosions carried out by the 
United States. In Australia, a group of seismologists was given ad- 
vance knowledge, and subsequently the relevant source data, on four 
nuclear tests carried out in central Australia. This information has 
been invaluable in leading to our first reliable knowledge of the 
broad structure down to a depth of 30 miles or so in a part of Australia. 
The United States hydrogen-bomb explosions of 1954 have proved to 
be of great interest, and have been the subject of special studies by 
T. N. Burke-Gaffney, Director of the Riverview Observatory (Syd- 
ney), and myself. 
About the middle of March 1954 news that a hydrogen bomb had 
been exploded was made public. Following this, information from 
Japanese fishermen indicated that the explosion had taken place near 
Bikini Atoll slightly before dawn on March 1, local time. This news 
made it feasible for a search to be made on a sufficiently limited stretch 
of the Riverview seismograms, and it transpired that there was indeed 
an isolated sharp movement near the expected time. The routine 
summary of seismic wave onsets recorded at Brisbane, 600 miles from 
Sydney, also reported a sharp movement in agreement with the River- 
view reading. 
This was enough to warrant an inspection of overseas seismological 
bulletins as they came in. It soon became evident that seismic waves 
from four of the 1954 hydrogen-bomb explosions had been distinctly 
recorded in at least 12 countries. Strangely enough, several of the 
observatories concerned had not realized that certain of their routine 
readings related to these explosions. 
When all the data were put together, we diagnosed what we felt to 
be the pattern of the explosions, and made estimates of the origin 
times. A recent release by the United States Atomic Energy Com- 
mission shows that our estimates were correct within 0.0, 0.1, 0.4, and 
0.7 second, respectively. The results have proved to have been of 
importance to geophysics in shedding further light on the earth’s 
inner core, and have supplied additional useful corrections to the 
travel-time tables. 
Further work on hydrogen-bomb explosions has been carried out by 
Gutenberg, Carder, Burke-Gaffney, and Rothé. 
Last September there was an interesting development following my 
presidential address to the International Association of Seismology 
and the Physics of the Earth’s Interior on the subject of “Seismology 
