376 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 19 31 



for this work comes from that part of the country where a sentiment 

 of wise preparedness for possible emergency is being developed. 



The purpose is to install instruments capable of recording accu- 

 rately strong earthquake motions in places where history indicates 

 that there is probability of earthquake activity of some intensity. 

 It is regrettable that such instruments were not installed in New 

 Zealand last February when invaluable information could have been 

 obtained. However, instruments of a satisfactory character were 

 not in existence, nor are they to-day, except for several types that 

 have been developed in Japan which are adapted to frequent, strong 

 activity (pi. 8, fig. 2). In this country the Bureau of Standards, 

 the Coast and Geodetic Survey, the Massachusetts Institute of 

 Technology, and the Earthquake Kesearch Laboratory at Pasadena 

 are all at work on the development of such instruments, and it is 

 expected that satisfactory instruments, even if not of the ultimate 

 type, will be available before the end of the present year. 



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I I II 11 II 111 I iiiriiMiBin I j 1 'yiTf] "iT ' II I I I I I 



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FiGunB 7. — Section of seismogram, actual size, recorded by a McComb-Romberg seis- 

 mograph, small model, on August 16, 1931, at Washington, D. C. Component, 

 N. 75 E. Time mark indicated by arrow point = ll hr. 45.0 miu., Greenwich civil 

 time. Epicenter : 30.0 N., 140.5 W. ; southwestern Texas 



It would be premature to describe instruments which, though in 

 process of development, have not yet been tested, but a few funda- 

 mental principles may be mentioned. 



It is not necessary to have elaborate piers separated from the floor 

 of the building, as for teleseismic instruments, but these strong 

 motion instruments may be placed directly on a basement floor or 

 preferably on a block of concrete resting on the floor. The principle 

 by which early recorders were set in motion by the earthquake, long 

 since abandoned because the important earlier and weaker phases 

 were lost, is being revived in different form. With a continuously 

 turning drum and with photographic recording started by the earth- 

 quake the objections are met, with resultant great economy of 

 operation. 



