EARTHQUAKE INTENSITY IN AUSTRALASIA. 271 



correction to Z.P. obtained from the reflections of stars is very 

 unsatisfactory, and there are grounds for believing that it is time 

 to discontinue the " double observation " of a star, and to adopt 

 some other method of reflection observation. Sir Charles Todd 

 proposes to select groups of stars, of which one (A) will be 

 observed directly, and another (B) by reflection, on one night, 

 whilst on tlie next B will be observed directly and A by reflection. 

 This will eliminate any error "due to comparatively violent usage 

 which a telescope must experience when a star is observed both 

 directly and by reflection on the same evening. 



5th. The law of, and the mean, refractions are not yet definitely 

 settled. !t would be well if all astronomers were to agree upon a 

 form of thermometer exposure, and if two or three northern and 

 southern observatories were to take a set of stars selected so as to 

 de ide these points as far as possible. 



-o-tji-o- 



5.— EARTHQUAKE INTENSITY IN AUSTRALASIA: 



WITH A FEW REMARKS OX THE TASMANIAN EARTHQUAKES, 

 SUGGESTED BY THE DIAGRAM OF INTENSITY. 



Bij GEORGE HOGBEX, M.A., Tlmaru, X.Z., Sccretdri/ Scisttiulogiccd 



Committee, A.A.A.S. 



Plate YII. 



Dr. Edward S. Holden, Director of the Lick Observatory, in a 



paper entitled " Earthquake Intensity in San Francisco " (American 



Journal of Science, June, 1888), has given the equivalents of the 



degrees of intensity of earthquake shocks on the Rossi- Forel 



scale, in terms of the acceleration due to the velocity of the shock 



itself, expressed in millimetres per second. These equivalents 



are : — 



Rossi-Fovel Intensity in 



Scale. Millimetres per Sec. 



1 20 



II 40 



III 60 



IV 80 



V 110 



VI 150 



VII 300 



VIII 500 



IX 1,200 



The absolute scale is calculated, on the assumption that earth- 

 quake motion does not diti^er greatly from simple harmonic, by 

 means of the formula — 



J V'- 47r"ff 



li "T^ 



