114 ILLINOIS ACADEMY OF SCIENCE. 



occurred on May 26, 1909. The latter was more extensive and 

 of greater severity than the one here described. This can readily 

 be seen by referring to the isoseismal drawing of the earthquake 

 of May 26, 1909, by Dr. J. A. Udden, in the Transactions of the 

 Illinois State Academy of Science for 19 10. In several instances 

 newspapers have made statements comparing the intensity of the 

 more recent earthquake to that of the former. The intensity for 

 cities lying within the mesoseismal area of the recent earthquake 

 is stated to be "equal to" or "more severe" than in the earlier 

 earthquake. Cities lying beyond the mesoseismal area describe 

 the earthquake as being less severe than that of May 26, 1909. 

 These statements conform quite satisfactorily with the isoseismals 

 of the two earthquakes. 



The epicentres of the two disturbances are differently located, 

 but the areas affected by both are substantially the same. By 

 referring to the drawings it is seen that the isoseismals of each 

 spread out from a nearly common center. The coincidence of 

 these two earthquake areas can hardly be regarded as a matter of 

 chance. It is probable that the two shocks were directly con- 

 nected with a gradual readjustment of the same strata. 



THE ROSSI-FOREL SCALE ACCORDING TO DUTTON. 



1. Microseismic Shock: Recorded by a single seismograph or 

 by seismographs of the same model, but not by several seismo- 

 graphs of different kinds ; the shock felt by an experienced 

 observer. 



2. Extremely Feeble Shock : Recorded by several seismo- 

 graphs of different kinds ; felt by a small number of persons at 

 rest. 



3. \'ery Feeble Shock : Felt by several persons at rest ; strong 

 enough for the direction or duration to be appreciable. 



4. Feeble Shock : Felt by persons in motion ; disturbance of 

 movable objects, doors, windows, creaking of ceilings; rattling 

 of dishes.* 



5. Shock of Moderate Intensity : Felt generally by everyone ; 

 disturbance, furniture, beds, etc., ringing of some door bells (old 

 style door bells) ; articles fall, dishes break."^ 



6. Fairly Strong Shock : General awakening of those asleep, 

 general ringing of bells, oscillation of chandeliers ; stopping of 

 clocks, visible agitation of trees and shrubs ; some startled persons 

 leave their dwellings. 



