MAGN BROGRAPH RECORDS. 
Several magnetographs at stations not very distant from the origin recorded the 
shock. ‘These have been examined by Dr. L. A. Bauer,' who finds that the time of dis- 
turbance on the magnetograph corresponds to the time of arrival of the principal part, and 
concludes, therefore, that the effect is entirely mechanical and not magnetic. The follow- 
ing table shows the time of the magnetograph records and the time of arrival of the 
regular waves, according to Dr. Bauer. 
TABLE 20. — Times of Magnetograph Records. 










STATION. DISTANCE. a Te be hate 
Sc h m. h. m. 
SILK aoe Dee 136229 32256 
Baldwin P Pw Ptic. 21.8 ila) pet BA 
(borermry 5 4 a 32.9 Ile Bays. CF GS HG 
Honolulttae-. ene 34.6 lia} Brae PUB. Pies 
Cheltenham .. . 35.6 1330 13a 30 
Porto Rico . : 53.4 Not recorded ee 

«The Toronto record was communicated by Mr. R. F. Stupart, director of the Canadian 
Meteorological Service. The records of the other stations are taken from Dr. Bauer’s article. 
? Time of the second preliminary tremors; the regular waves are 3.4 minutes later. 
3 Not determined from the seismogram, but from the hodograph curve, plate 2. 
It will be seen that the magnetographs recorded only during the time of the strong 
motion, which convinces us that they acted mechanically like seismographs, for if they 
had been affected by a magnetic disturbance due to the earthquake, the effect would 
have been produced long before the arrival of the slow surface waves; indeed, before 
the arrival of any elastic waves in the mass of the earth. The maximum disturbance 
of the Toronto declination needle occurred at 13" 33.6"; and the maximum recorded by 
the seismogram at 13” 33.3™. 
Baldwin, Kansas (lat. 38° 47’ N., long. 95° 10’ W.), is the only one of these stations 
that did not have a seismograph; and the magnetograph record began about 1.5 minutes 
after the regular waves must have reached there according to the hodograph. Being in 
the middle of the United States, far from any seismographic station, an accurate record 
at Baldwin would have been valuable; but the time scales of magnetographs are too 
small to yield close time values; and they do not, in general, record before the strong 
motion. The Baldwin record is therefore only valuable in so far that it does not contradict 
the results obtained from regular seismographs; and we can not hope that magnetograph 
records in the future will, in general, be important additions to the records of seismo- 
graphs. 
1“ Magnetograph Records of Earthquakes with Special Reference to the San Francisco Earthquake.” 
Terrest. Magn. and Atmos. Elect., 1906, vol. x1, pp. 135-144. 
139 
