ON SEISMOLOGICAL INVESTIGATION. 249 



been realised. The shock of the impact of the meteorites on the earth was registered 

 as an earthquake, not only at Irkutsk, Tashkent and Tiflis, but as far away as Jena. 

 On the other hand human beings were much less affected by the earth movements 

 than by the waves of pressure in the atmosphere. There is no other known instance 

 of an earthquake produced bj' the action of a meteor, as indeed there is no record in 

 historic times of a meteor devastating an area of hundreds of square miles, of a meteor 

 producing airwaves which could travel a quarter of the way round the globe or of 

 a meteor transforming the sky and prolonging twilight in middle latitudes right 

 through the night. 



The seismic effects of the meteor have been discussed also by E. Tams {Zeitschrift 

 der OeseUschaft fiir Erdkunde zu Berlin, 1929, pp. 143-5). Tarns found that the 

 seismic waves had been registered at Hamburg, and estimated that the movement 

 of the ground north and south had had an amplitude of about Ifx. He states also 

 that the vertical oscillations recorded at Jena on the Straubel seismograph had an 

 amplitude of 2-3jji. From these new data it may be deduced* that the energy of the 

 aerial waves was about 5,000 times that of the seismic ones. 



The Broadcasting of Seismological Information. 



The practice has been continued of broadcasting information with regard to large 

 earthquakes registered at Kew Observatory. Reports are communicated to the 

 Meteorological Office, Air Ministry, and are broadcast from Kidbrooke at 14h. or 

 19h. G.M.T. with the meteorological data which are normall}' being sent out at those 

 hours. By special arrangement similar reports of earthquakes registered at Bombay 

 are communicated to London and are also broadcast from Kidbrooke at the first 

 opportunity. 



The reports for Strasbourg (broadcast from Eiflfel Tower), from Helwan (broadcast 

 from Cairo), and from selected American stations (broadcast from Arlington) are 

 received at the Air Ministry. Persons wishing to have such reports communicated to 

 them regularly should apply to the Director of the Meteorological Office. 



During the year ended March 31, 1930, reports of earthquakes registered at Kew 

 Observatory were broadcast on twenty-two occasions. In five cases the estimated 

 position of the epicentre was stated. In the same period Bombay reports were broad- 

 cast on eleven occasions. Messages were received from America through the Air 

 Ministry on thirteen occasions. 

 July 'l 8, 1930. 



* The seismic waves were large enough to be recorded at Hamburg for two minutes. 

 No doubt sufficiently sensitive apparatus would have sho-nn a disturbance lasting 

 much longer. Considering the distance, about 50°, the long wave phase of the earth- 

 quake might be expected to last about 40 minutes. Remembering that the energy 

 depends upon the square of the amplitude, an estimate of the total energy as 10 times 

 that passing in the two minutes of greatest disturbance appears reasonable. The 

 expression given by Jeffreys for the total energy crossing a small circle at distance A 

 from the origin of an earthquake is equivalent to 



l-12x(2Tc)''RpsinA('«'^'„^ 



In this expression R is the radius of the earth, p is the mean density of surface 

 rocks (3 gm./c.c), a is the amplitude of the horizontal motion, V and T are the velocity 

 and period of the waves. 



Substituting a= V'2x 10-^ cm., V=3x 10= cm./sec, T = 15 sec. and ^=120 sec, 

 we find 6x lO^* ergs for the energy passing in two minutes and 6x 10"' ergs for the 

 total. 



The energy of the air waves was previously found to be of the order 3 x lO^" ergs — 

 Q.J. Met. Sac., 56 (1930), 300. 



F. J. W. W. 



