ftATE OF TRANSLATION OF THE WAVE. 81 



CHAPTER VII. 



OF THE RATE OF TRANSLATION OF THE WAVE. 



We would at once declare that, in the present state of earthquake 

 enquiries, the determination of the transit velocity of the shock, that 

 is, the rate at which the wave-form is transmitted from part to part of 

 the perceptibly shaken portion of earth's surface, appears to us of minor 

 importance, and we shall not therefore delay to discuss it in much detail. 



In truth, the difficulties which we have already indicated, as affecting 

 our observation of the shock at all, the comparatively wild and unin- 

 habited nature of the country, the absence of most of those ordinary 

 indices of civilisation which could become the permanent indices of the 

 extraneous forces applied to them and resulting" in their overthrow or 

 destruction,— all these difficulties combined with others most seriously 

 affect any observations, which seek for precise and accurate measurements 

 of time. Where the motion of transit is so rapid, as in the case of great 

 earthquakes, that even fractions of a second become essentially important 

 in ascertaining the true rate, it seems almost absurd to think of depend- 

 ing upon the ordinary measurements of time, by clocks in every-day use, 

 unregulated and often differing by not only seconds, but minutes or even 

 hours from the true time. During my own experience in India I have 

 known the station gun — the gun usually fired with the intention of 

 indicating midday in the more important military stations — to vary 

 from the true mean time by not less than 53 minutes. I have more 

 than once seen sun-dials which had been removed from one station to 

 another, these stations differing in their latitude by four or five degrees, 

 and reset the meridian being obtained by the use of a common magnetic 

 compass without any consideration of variation, and the inclination of 

 the gnomon left quite unaltered, and still the instrument trusted 

 to in one place quite as unhesitatingly as in the other, and it is by no 

 means an uncommon thing to find persons, who have really good watches, 

 abandon the use of them, and trust to the gong or ghurri of the 

 e ( 81 ) 



