680 



SCIENCE. 



[N. S. Vol. XII. No. 305. 



calls attention to the fact that injury to brick 

 buildings by earthqualses is nearly always 

 much greater in the upper stories than in the 

 lower, and he illustrates this by photographs of 

 the condition after the great earthquake of 

 1891 of the Aichi Cotton Mill and the Post and 

 Telegraph Office, both at Nagoya. The Charles- 

 ton earthquake in 1886 afforded many examples 

 of this. 



Omori furnishes two very interesting notes on 

 the great earthquakes of 1891 and 1894. These 

 are the most violent disturbances that Japan 

 has suffered in recent years, and that of October 

 28, 1891, was probably at least equal in inten- 

 sity to any other earthquake of which we have 

 authentic record. Its greatest activity was dis- 

 played in the provinces of Mino and Owari. 

 The land area disturbed was about 250,000 

 square kilometers, and as the mean radius of 

 propagation was about 520 kilometers the total 

 shaken area was about double the area of the 

 whole empire. The total number of people 

 killed was 7,000, and 80,000 houses were en- 

 tirely destroyed. The fact that only one life 

 was lost for every 11 houses destroyed illustrates 

 (when compared with the effects of earthquakes 

 in brick- and stone-building countries) the 

 greater safety of wooden houses which,- even 

 when destroyed, afford ample warning and 

 time to enable their inmates to escape. 



' The actual motion in this earthquake was no- 

 where satisfactorily recorded on seismographs, 

 but Omori has made up for this lack as far as 

 possible by the observation and calculation of a 

 large number of overturned stone lanterns and 

 tomb stones, noting as well those not over- 

 turned. The horizontal acceleration necessary 

 to overturn is calculated by West's formula 

 which is very simple and unquestionably very 

 nearly correct under the conditions considered. 



It is 



X 



a = — a 



in which g is the acceleration due to gravity, 

 and X and y the horizontal and vertical coordi- 

 nates of the center of gravity of the column, the 

 origin being the edge about which overturning 

 takes place. It is assumed that the motion is 

 entirely horizontal which introduces no sensible 

 error except for points, very near the epifocus. 



Results are computed for about sixty points in 

 the disturbed area, and in several instances a 

 horizontal acceleration of over 400 centime- 

 ters per second, is shown. The seismograph at 

 Nagoya, one of the principal points shows that 

 the complete period of the principal vibra- 

 tions was about 1.3 seconds, and as the maxi- 

 mum acceleration there was 260 cm., it follows 

 that the range or amplitude of vibration of the 

 earth particle was between 23 cm. and 24 cm. 



The earthquake of June 20, 1894, although 

 the most violent experienced in the Tokyo dis- 

 trict since 1855, was much less strong than that 

 of the Mino-Owari district referred to above. 

 Twenty-six persons were killed and 171 were 

 wounded. Fortunately the disturbance was 

 very satisfactorily recorded by a strong-motion 

 seismograph at the Seismological Observatory 

 in Tokyo. The actual amplitude of horizontal 

 motion was 7.3 cm., and the maximum ac- 

 celeration was about 100 cm. per second. In the 

 greater shock of 1891 this was probably not less 

 than 1,000 cm. per sec. per sec. — being a little 

 greater than the acceleration due to gravity. 



Dr. H. Nagaoka has a very interesting paper 

 on the experimental determination of the elastic 

 constants of rocks, leading to important conclu- 

 sions relating to the velocity of seismic waves. 

 From observations made in Italy and also in 

 Japan, Omori has concluded that the velocity 

 of the first tremor is generally as high as 13 kilo- 

 meters per second, which is surprisingly great, 

 the principal shocks usually showing a speed of 

 3 kilometers to 4 kilometers per second. 



Nagaoka discusses the conditions under which 

 the very high velocities may occur, and one 

 cannot avoid being impressed with the great 

 value of earthquake observations as a means of 

 ascertaining the nature and conditions of the 

 interior of the earth. 



The greatest part of No. 4 consists of an ac- 

 count, by Omori, of an elaborate series of 

 ' Experimental Studies upon Fracturing and 

 Overturning Columns,' and this is not only one 

 of the most interesting, but perhaps the most 

 important paper in the whole series. In this 

 investigation the ' shaking table ' already re- 

 ferred to was made use of and columns of con- 

 siderable dimensions and various materials were 

 used. Many were of dimensions equal to those 



