246 JOURNAL OF SCIENCE. 



For the purpose of accurate observation of earthquakes the 

 immense advantages of a system of standard time and the habit 

 of referring to that time are sufficiently shown by a comparison of 

 of the respective reports of the Charleston Earthquake of 1886 and of 

 the East Anglian Earthquake of 1884. These advantages are still 

 further emphasise! by a reference to a paper in the "Geological 

 Magazine " of the present year (On the British Earthquakes of 1889, 

 by Charles Davison, M.A.) It is true that the areas over which the 

 earthquakes investigated were felt were so small that very accurate 

 time-observations would have been required to determine the epi- 

 centrum ; but the nature of the time-notes taken shows generally that 

 the opportunities for good time-observations are fewer in Great Britain 

 than in New Zealand. 



The interesting point for us is the careful way in which the 

 epicentrum is determined by the intensity of the shock at various 

 places — namely, by drawing isoseismals (or lines on the map so as to 

 pass as nearly as possible through places where the intensity was the 

 same). As the chief mode of finding the origin of a shock this is more 

 likely to be successful in thickly-settled countries ; nevertheless, it 

 might be useful in these colonies to supplement and correct inferences 

 derived from time-observations. 



It is necessary, of course, that the same way of describing degrees 

 of intensity should be. employed by all observers. Nothing better, 

 probably, can be suggested than the Bossi-Forel scale used by Mr. 

 Davison. He gives a translation of it (reprinted below), and remarks 

 thereon : " This scale is very generally adopted by Italian and Swiss 

 seismologists, and, though rough and undoubted^ variable to a slight 

 extent, is well suited to the nature of the evidence at our disposal, the 

 range of variability of any degree of the scale being probably less than 

 the limits of error of ordinary observations." 



Bossi-Forel Scale of Intensity. 



I Becorded by a single seismograph, or by some seismographs of 

 the same model, but not by several seismographs of diffeient kinds; the 

 shock felt by an experienced observer. 



II. Becorded by seismographs of different kinds ; felt by a small 

 number of persons at rest. 



III. Felt by several persons at rest ; strong enough for the 

 duration or the direction to be appreciable. 



IV. Felt by persons in motion ; disturbance of moveable objects, 

 doors, windows, cracking of ceilings. 



V. Felt generally by everyone; disturbance of furniture and beds, 

 ringing of some bells. 



VI. Generally awakening of those asleep ; general ringing of bells, 

 oscillation of chandeliers, stopping of clocks ; visible disturbance of trees 

 and shrubs. Some startled persons leave their dwellings. 



VII. Overthrow of moveable objects, fall of plaster, ringing of 

 church bells, general panic, without damage to buildings. 



VIIT. Fall of chimneys, cracks in the walls of buildings. 



IX. Partial or total destruction of some buildings. 



X. Great disasters, ruins, disturbance of strata, fissures in the 

 earth's crust, rock-falls from mountains. 



