﻿8 C. G. Rockwood, Jr. — American Earthquakes. 



Destructive, in the same sense as in my last notes (this Journal, 

 xxix, 426); but I have added a Koman numeral to indicate 

 the intensity according to the Eossi-Forel scale* adopted by 

 the Italian and Swiss seismologists. The two scales may be 

 compared thus : 



Very light — II or III. 



Light " = IV. 



Moderate =. V or VI. 



Strong = VI or VII. 



Severe = VIII. 



Destructive =. IX or X. 



1885. 



Jan. 2. — 21 h 12 m , a light earthquake (IV) occurred in Frederick 

 County, Maryland, and Loudon County, Virginia, and adjacent 

 districts. It was most severe in the southern part of Frederick 

 County and affected an oval area of about 3,500 square miles, 

 whose boundary just included Boonesborough and Newmarket, 

 Md., Washington, T>. C, and Warrenton, Va. The noise accom- 

 panying the' shock was compared to that made by a loaded wagon 

 passing rapidly over frozen ground or over a bridge, to distant 

 thunder, and to the roaring of a chimney on fire. In some cases 

 persons went out of their housesto see if their chimneys were not 

 burning. The estimates of the duration of the shock were as 

 usual very discordant, varying from two seconds to two minutes. 

 As the tendency is to exaggerate this element, probably ten or 

 fifteen seconds would be a liberal estimate of the duration. A 

 fuller notice of this earthquake, with a map, was published in 

 Science, v, 129. 



* As this scale is not very readily accessible in America (it was printed in 

 Science, v, 197), I reproduce a translation of it here for reference in connection 

 with these papers. 



I. Microseismic shock. — Recorded by a single seismograph or by seismographs 

 of the same model but not putting in motion seismographs of different patterns ; 

 reported by experienced observers only. 



II. Shock recorded by several seismographs of different patterns; reported by 

 a small number of persons at rest. 



III. Shock reported by a number of persons at rest; duration or direction 

 noted. 



IV. Shock reported by persons in motion; shaking of movable objects, doors 

 and windows ; cracking of ceilings. 



V. Shock felt generally by every one ; furniture shaken ; some bells rung. 



VI. General awakening of sleepers; general ringing of bells; swinging of 

 chandeliers; stopping of clocks ; visible swaying of trees; some persons runout 

 of buildings. 



VII. Overturning of loose objects; fall of plaster; striking of church bells; 

 general fright without damage to buildings. 



VIII. Fall of chimneys ; cracks in the walls of buildings. 



IX. Partial or total destruction of some buildings. 



X. Great disasters ; overturning of rocks; fissures in the surface of the earth; 

 mountain slides. 



