n8 POPULAR SCIENCE MONTHLY 



other hand, the equally large earthquake of January 31, last, the 

 origin of which was at sea off the west coast of Ecuador, besides record- 

 ing itself on seismographs the world over was recorded on the mag- 

 netographs at Baldwin, Porto Rico and Cheltenham, but this time not 

 at Honolulu. This seaquake was accompanied by a tidal wave twenty 

 feet high which rushed in on the coast of Ecuador, causing great de- 

 vastation; it set the Pacific Ocean in vibration, which according to the 

 tide-gauge records of the Coast and Geodetic Survey at San Diego and 

 Honolulu lasted for three days. The tidal wave, when it rushed in on 

 the Hawaiian coasts, was several feet high, and the record of this quake 

 of January 31, as recorded on the Milne seismograph at the Honolulu 

 Magnetic Observatory, was among the largest since the installation of 

 the instrument, September, 1903, and yet the delicately suspended 

 magnets, as far as the magnetic records at this observatory would 

 indicate, were not affected. 



Why is it that an earthquake will at times be recorded by magnetic 

 instruments and at other times leave no record? Or, to go back to 

 the fundamental question, what do the magnetic instruments record — 

 an actual mechanical effect due to the mechanical vibration of the point 

 of support ? If the observed effect is a purely mechanical one, then 

 why is it that not every mechanical disturbance is recorded on the 

 photographic records of the fluctuations of the magnetic needles? 

 What is the characteristic of the mechanical vibration, the presence or 

 absence of which in the earth movements is responsible for the presence 

 or absence of the effect recorded by magnetic needles? 



The solution of these questions may show the magnetograph to be 

 a most useful adjunct to the present instrumental equipment for re- 

 cording earth movements. 



Is the possibility of any actual magnetic effect accompanying an 

 earthquake entirely to be excluded? If so, in the case of the distant 

 earthquakes, as seems probable, is the possibility also to be excluded 

 for the less distant ones, or say for stations within a certain prescribed 

 region about the origin of the quake? Are those cases where records 

 are secured on magnet ographs and not on seismographs to be attributed 

 possibly to such a magnetic effect which has no influence on instruments 

 responding merely to mechanical vibration? Or is it possible that the 

 magnetograph is in certain cases a better micro-seismograph than the 

 Milne or Bosch-Omori instruments used in this country? 



We have thus some extremely interesting questions presented to us 

 which, however they may be solved, will be a valuable contribution to 

 our knowledge of earth movements. The possibility might also be 

 mentioned that an approaching earthquake might through electric or 

 magnetic effects give the first indication on magnetographs because of 

 the much greater velocity of propagation of such effects than that 



