246 HOVEY— EARTHQUAKES : [April 24. 



consists of ten degrees of intensity and depends upon human ob- 

 servers and the effects upon buildings for the classification of a 

 shock. 



On account of the vagueness of these series, the influence of the 

 personal equation of the observer in placing shocks in accordance 

 with them and the over-importance attached by them to effects upon 

 human property, other scales have been proposed, the best of which 

 are based upon instrumental records. Difficulties in using the 

 latter, however, arise through the small number of instruments 

 actually at work, and the Rossi-Forel and Mercalli scales are still 

 found very useful, particularly in the collection of data. 



I shall close what I have to say regarding the subject of the 

 afternoon by brief descriptions with illustrations of the earthquakes 

 that occurred at Charleston, S. C, in 1886, at San Francisco in 

 1906, at Kingston, Jamaica, in 1907, and at Messina in 1908. 



The Charleston Earthquake. 



The most important earthquake occurring in the eastern part 

 of North America during the historic period was that which de- 

 vastated Charleston, South Carolina, in 1886. This was investigated 

 under the auspices of the United States Geological Survey by Major 

 Clarence E. Button and his assistants, their report being published 

 in the Ninth Annual Report of the survey. 



About eight o'clock in the morning of August 27, 1886, the 

 villagers of Summerville, 22 miles northwest of Charleston, S. C, 

 were startled by the noise and shock of what was at first thought to 

 be a heavy blast or a boiler explosion. The sound seemed very 

 near, but no cause for it was learned that day. Around five o'clock 

 the next morning the noise and shock came again and more heavily, 

 and the idea that an earthquake had occurred became general and 

 was strengthened by light tremors that were felt that day and the 

 next. The affair seemed then to be over, for nothing unusual was 

 heard or felt on the thirtieth and during daylight of the thirty-first. 

 The noises or shocks were felt by very few people in the city of 

 Charleston, but they were the premonitions of the great earthquake 



