164 REPORT— 1897. 



Earthquake Iso. 67 (November 5, 1896). 



Sliidc Records : h. 



Preliminary tremors commence 9 



,, „ duration 



Maximum .... 



Duration of disturbance about 

 Mcolaiew, commencement 

 Ischia, „ 



Earthquake No. 73 (Severn Valley). 



SJtide Records, December 16, 1896. 



The earthquake which created so much alarm in the Severn Valley 

 at about 5.. 30 a.m. on December 17, when chimneys were shattered and 

 certain buildings more or less unroofed, was only barely perceptible in 

 the Isle of Wight. The booms of the seismographs at Shide were not 

 slowly tilted from side to side, as is the case when they record earthquakes 

 originating at a great distance, but merely set in a state of elastic vibra- 

 tion, behaving, in fact, like the pointers of seismographs intended to 

 record movements which we feel. The range of these elastic movements, 

 for the most part, were about 1mm., and did not exceed 3 or 4mm. One 

 marked motion commenced at 17h. 30m. 55s., and lasted 5 minutes. 



These tremors, which were intermittent and not continuous, as is 

 the case in an ordinai-y tremor storm, commenced about 11 p.m. on the 16th, 

 and ended at about 1 1 a.m. next morning. The duration of each group 

 was from 1 to about 6 minutes, and they were separated by intervals of 

 5 to 60 minutes. Twenty-two of the tremor groups shown by one instru- 

 ment apparently closely agree in time with 22 maxima shown by a second 

 instrument in another room. 



Because there were certainly movements or phenomena observed 

 indicating movements of the ground before and after the chief shock, 

 the approximate times at which a few of the twenty-two groups of 

 tremors were noted are here given. 



December 16 : at about 11 hrs. ; after 14 hrs. ; at 15 hrs., two 

 groups ; 16 to 18 hrs. an intermittent series, with a maximum about 

 17h. 30m.; between 18 to 19 hrs., two groups; and the last at about 

 22 hrs. 



Should it be found necessary, the exact time of each of these may be 

 computed from the original photograms. 



Details connected with many observations contained in the first two 

 columns will be found in ' Symons's Meteorological Magazine,' January 

 1897. These observations indicate that during the night of December 16 and 

 17 persons living in widely separated districts were from time to time dis- 

 turbed by what they considered to be a tremulous motion of the ground. 

 Because it was night time, in no instance that I am aware of can it be 

 assumed that accurate time observations were made ; and, therefore, a 

 few of them have been bracketed together, as possibly referring to the same 

 disturbance. 



The Leicester and Hampshire observations, made between 9.30 a.m. 

 and noon, strangely enough, were the result of observing similar pheno- 

 mena, namely, the twitching of telegraph wires. In Leicester this was 

 seen by a number of persons, the wires vibrating vertically in an unusual 

 and extraordinary manner, there being no wind or other cause to which 

 the movement could be attributed. 



