LSOSEISTS. DISTRIBUTION OF INTENSITY, ETC. 89 



buildings. (Owing to poor material and construction in India 

 damage to buildings is considered to begin here.) 



VIII. — Very Strong Shock— fall of chimneys, cracks in walls of 

 buildings. 



IX. — Extremely Strong Shock — partial or total destruction of 

 some buildings. 



X. — Shock of Extreme Intensity — great disasters, ruins, disturbance 

 of strata, fissures in the earth's crust, rock falls from mountains. 



A revised and simplified scale was adopted by the Commission 



appointed to investigate the California Earth- 



Scaioadopicxi l.yihc k( , of A nl 18th.' 1900. Degrees VIII, IX 



Cahforman Commission. ■> ' > 



and X agree with the above. The first seven 



are as follows : — 



I. — Perceptible — only by delicate instruments. 

 II. Very Slight Shock — noticed by a few persons at rest. 

 HI. — Slight Shack of which direction and duration were noted 



by a number of persons. 

 IV. — Moderate Shock reported by persons in motion ; shaking 

 of movable objects ; cracking of ceilings. 

 V. — Smart Shock generally felt; furniture shaken; some clocks 

 Stopped ; some sleepers awakened. 

 VI. — Severe Shock — -general awakening of sleepers ; stopping of 

 clocks, some window glass broken. 

 VII. — Violent Shock — overturning of loose objects; falling of 

 plaster ; striking of church bells ; some chimneys fall. 



There are many uncertain features about both schemes. The 



personal factor of course enters very largely, 



^WsadTantagea of the ^ different observers interpret the same event 



in different ways. The Commission point out 

 that the stopping of clocks is a very uncertain criterion of 



intensity, a statement well substantiated in the present case too. 

 Again, with regard to degrees VI, VII, VIM and IX of the Rossi- 

 Forel scale, in which damage to buildings is relied upon for an 

 estimate, two important factors are given which tend to vitiate the 

 conclusions arrived at as to comparative intensity. These are, 

 the great variability of the Structures themselves, and the nature 

 of the ground upon which they are built. The scale was probably 

 designed originally for regions where brick and masonry struc- 

 tures prevail; in California wooden structures are by far the most 



