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 Rossi-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 unfelt? 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, 
