THE EARTHQUAKE OF MAY 26, 1909 157 



however, clearly indicated by reports from which the intensity of the 

 motion may be estimated, and from which isoseismal lines may be 

 constructed. 



The data contained in the press reports can be readily compared 

 with the Eossi-Forel scale of intensities. The greatest intensity shown 

 is in the falling of chimneys and in the cracking of walls, which barely 

 approximates eight in the scale. It is not practical to separate these 

 localities of greatest intensity from a more extended region where the 

 earthquake had an intensity more nearly comparable with seven in the 

 scale. Within this area furniture was overthrown, plaster fell from 

 ceilings and from walls, and hanging pictures and other suspended 

 ornaments were jerked loose from their fastenings. Outside of this 

 most severely disturbed mesoseismal area there is a belt from ten to a 

 hundred miles wide where the intensity approximates the next lower 

 point in the scale. Here lighting fixtures, chandeliers and bookcases 

 are reported to have swayed, dishes were broken, chairs rocked or were 

 moved or overthrown, houses were rocked, chimneys cracked and clocks 

 were stopped. Beyond this again is a zone where the evidence of the 

 earthquake consisted in the more subdued motions described as shaking 

 of houses and of furniture, rattling of dishes, bottles and tinware and 

 swinging of suspended objects. This zone has a width of from fifty 

 to a hundred and fifty miles and marks the location of the fifth iso- 

 seismal. Continuing the diminuendo, the earthquake next announced 

 its rapid passage by the rattle of windows, the jarring and quivering 

 of houses, and by gentle shaking and trembling of furniture. This is 

 the fourth intensity, and characterizes a zone that merges imperceptibly 

 into the next, where few people noticed the disturbance, and where it 

 appeared as a merely perceptible jar, or a slight undulation, most fre- 

 quently noted only in the upper stories of high buildings. In this 

 gentle form it disappeared to human senses at a distance, in all direc- 

 tions, of some four hundred miles from the central region. How much 

 farther did it speed, unseen, unheard and unf elt ? You will remember 

 that it left a record on the seismometer in Washington. This city is 

 nearly four hundred miles beyond the zone where the waves ceased to 

 be perceptible to the unaided human senses. From this record we may 

 infer that in the brief span of two or three minutes the earthquake 

 waves spread over a circular area about sixteen hundred miles in 

 diameter. 



A classified review of the little things that happened in the upper 

 Mississippi Valley, when a block of the earth slipped in the northern 

 part of Illinois may perhaps be of interest. The phenomena reported, 

 affected at least five of the human senses, the senses of general well- 

 being, of touch, of equilibrium, of hearing and of sight. 



A rheumatic woman in the zone where the disturbance was very 

 feeble "felt the vibrations keenly and told others of the earthquake, 



