Scales of Seismic Intensity. 47 



appointed by the Helvetic Society of Natural Sciences in 

 1878. 



1. Shock of microseismometric order. 



2. Extremely feeble shock, noted only by seismometric 

 instruments. 



3. Very feeble shock, perceptible to a person awake and. 

 in a peculiarly favourable condition for observation, at rest, 

 lying down, &c. 



4. Feeble shock, perceptible to persons awake and moving 

 about, capable of waking persons who are asleep ; making 

 suspended objects or liquids oscillate. 



5. Shock o£ moderate intensity, displacing movable objects. 



6. Rather strong shock, upsetting furniture, making 

 fissures in the walls and ceilings of houses. 



7. Strong shock, damage to houses, chimneys thrown 

 down. 



8. Yery strong shock, outhouses and huts thrown down. 



9. Extremely strong shock, well-built houses thrown 

 down. 



10. Shock of extreme intensity, disturbance of strata, 

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



(6) Rossi-Forel Scale.— -M. S. de Rossi, Bull. Yule. Ital., 

 Anno X. 1883, pp. 67-68 ; F. A. Forel, Arch, des 

 Sci. phys. et nat., vol. xi. 1884, pp. 148-149. 



Shortly after the preceding scale was drawn up, M. Forel 

 became acquainted with the earlier one employed by de Rossi. 

 On the invitation of the latter seismologist, they united in 

 revising both scales ; and the result will probably form the 

 foundation of seismic scales for many years to come. The 

 Rossi-Forel scale has been used in Italy until within the last 

 few months. It is the standard of earthquake intensity used 

 by seismologists in Switzerland, Great Britain, Roumania, 

 Greece, California, and Australasia. Rough and imperfect, 

 as no doubt it is, this scale has formed the starting-point of 

 a distinct advance in the study of earthquakes. 



Prof. E. S. Holden, who has done so much for the investi- 

 gation of Californian earthquakes, has made a comparison 

 between each degree of the Rossi-Forel scale and the 

 corresponding maximum acceleration of an earth-particle 

 calculated from seismographic records. His results will be 

 found in the last column of the table given below *. 



1. Recorded by a single seismograph, or by some seismo- 

 graphs of the same pattern, but not by several seismographs 

 of different kinds ; the shock felt by an experienced observer. 

 * Amer. Joum. Sci. vol. xxxv. 1888, p. 429. 



