302 



EARTHQUAKES. 



in some places, rising in others, and being agi- 

 tated everywhere. 



3. The volcanic theory, which holds that 

 the disturbances are due to fires in the earth's 

 center, and to their fumes and steam, which 

 force an outlet. In the hot water, steam, and 

 gas ejected, and in the odors imparted to 

 springs and wells, they find evidence of the 

 truth of their theories. 



4. The astronomical theory, which holds 

 that the cause is to be found in the attraction 

 of the planets, derives argument from the 

 enormous weight of extraordinary tides, and 

 claims that the attraction of the sun and the 

 moon operates on the crust of the earth as it 

 does on the great body of water that it raises 

 or lowers. Much discredit has been cast upon 

 this theory by charlatans who have pretended 

 to foretell earthquakes from the stars. 



5. The electrical theory, whose followers 

 will deduce from the lights, noises, and veloci- 

 ties of their motions, and from comets and 

 meteors that have appeared simultaneously 

 with the earthquake, conclusions favorable 

 to the origin of the disturbance from that 

 subtile and universal agent, electricity. Thus, 

 for example, an earthquake occurred in Con- 

 necticut on Aug. 9, 1840, and at the same time 

 occurred an unusual fall of meteors, numbered 

 by a writer in the " American Journal of 

 Science and Arts" as high as 1,500, for the 

 night of the 9th. It is curious to observe 

 that on Feb. 2, 1766, in Rhode Island and 

 Massachusetts, and in November of the same 

 year at Charleston, S. C., and at Weston, 

 Conn., in December, 1807, a similar coinci- 

 dence was remarked. 



6. The chemical theory, which ascribes the 

 disturbance to fermenting or decomposing 

 minerals. A curious instance of decomposition 

 of crystalline rocks is reported by Dr. Hunt. 

 They were principally gneisses with hornblend- 

 ic and micaceous schists, and are completely 

 decomposed to a depth of fifty feet or more 

 from the surface, being changed into an unc- 

 tuous, reddish brick-clay, in the midst of 

 which the interbedded layers of quartz are 

 seen retaining their original positions. The 

 believer in the conversion of metallic potassi- 

 um, by rapid inflammation, into common pot- 

 ash in the deep recesses of the earth, finds in 

 the saltpatrous sandstone an argument for his 

 belief in the chemical theory of earthquakes. 



Observations. It is much to be regretted that 

 phenomena accompanying seismic disturbances 

 have been hitherto so imperfectly noted. The 

 manner in which these workings of Nature re- 

 veal themselves to us have such a powerful 

 influence upon the imagination and under- 

 standing that few people are sufficiently calm 

 and collected to report fully the attendant cir- 

 cumstances. The lack of any definite bureau 

 to which information could be forwarded by 

 individual observers was also a powerful factor 

 in maintaining the state of ignorance on this 

 subject, and to obviate this want the Director 



of the Geological Survey called a meeting at 

 Washington on Nov. 21, 1884, to consider and 

 arrange a systematic plan of earthquake-ob- 

 servation throughout the country. It was de- 

 cided to attempt work in two directions: 

 First, by the distribution of circulars, which 

 were to be tilled up by individual observers and 

 returned to the Geological Survey after the 

 occurrence of an earthquake ; and, secondly, 

 the establishment of stations, provided with 

 instruments for recording the earth's motion. 

 The address, to which inquiries and facts of in- 

 terest can be sent, is Division of Volcanic Ge- 

 ology, U. S. Geological Survey, Washington, 

 D. G. 



An attempt has been made to distinguish, 

 by the use .of adjectives, the relative degrees 

 of intensity of shocks, and the following table 

 has been prepared for the use of observers : 



1. Very light. Noticed by a few persons, 

 but not generally felt. 2. Light. Felt by a 

 majority of persons, rattling windows and 

 crockery. 3. Moderate. Sufficient to set sus- 

 pended objects, as chandeliers etc., swinging, 

 or to overthrow light objects favorably placed. 

 4. Strong. Sufficient to crack the plaster in 

 houses, or to throw down bricks from chim- 

 neys. 5. Severe. Overthrowing chimneys or 

 walls and injuring some buildings. 6. Destruc- 

 tive. Causing general destruction of buildings, 

 etc. It is hoped that future observers will 

 use this scale in their reports to the Geological 

 Survey. The following suggestions are made 

 by the Geological Survey to observers : " State 

 the observer's situation whether in the house 

 or out-of-doors, up stairs or down, sitting, 

 standing, walking, reading. Then answer the 

 following questions, referring to them by 

 number only: 1. Was an earthquake felt at 

 your place? 2. At what hour, minute, and 

 second, and whether railway or local time? 

 3. How long did you perceive it? 4. Was it 

 accompanied by any unusual noise? If so, de- 

 scribe it. 5. Give, as accurately as possible, 

 the number, duration, and character, of each 

 shock. 6. Specify it according to the table of 

 intensity light or very light, etc. 7. Do you 

 know of any cause for what happened, other 

 than an earthquake ? Give any further par- 

 ticulars of interest, stating whether they are 

 from observation or hearsay. Mention the 

 condition of the atmosphere; any strange ef- 

 fects on animals ; character of damage to build- 

 ings; general direction in which walls, chim- 

 neys, etc., fell. Springs, rivers, and wells, are 

 often noticeably affected, even by slight shocks. 

 Describe the direction in which chandeliers, 

 etc., swung. If pictures swung, state the di- 

 rection of the wall, and whether pictures on 

 the wall at right angles to it were also moved. 

 If doors were opened or shut, state the direc- 

 tion of the wall in which they were set. 



Seismometers, or instruments for recording 

 earthquake - shocks have been frequently in- 

 vented and used. Briefly stated, the govern- 

 ing principle of them all is either a pendulum, 



