EARTHQUAKE MEAöUKEMEXTsi IN I'lT AXiJ OX 8UKFACE. 



1>83 



This tabic .'seem.s In shew that li»i- . mnll (':iflh(jiiak(,'.< the aiii|)htiide 

 aiid the period are oii the \vh(j]e nearly tlie same on the free surface 

 and in the pit, there Ijcing a slightly greater motion on the surface. 

 This confirms the result which Prof. Milne previously obtained. In the 

 above are not included those very small earthquakes, whose measure- 

 ments are difficuH ; these li(_)\vever shew tliat the motion in the pit 

 is also small when tlie motii^n obser^■ed on tlie surf see ground is small. 



It must l)e noticed that the diagram taken in the pit appears 

 always to be smofjther tlian that obtained on the surface, and //, or 

 the number of irregular wavelets occurrinii' in 10 seconds, is f )und 

 in every case t(j l:ie greater for the latter, l)eing often twice as manv as 

 for tlie former. 'J'his is very remarkaldy shown in the three severe 

 earthquakes mentioned above, for which calculât ioii;; ha\e Ijcen made 

 separately as regards large undulations and small ;;uperposed ripples. 

 The ratios of the amplitudes, peric)ds, maximum velocities, and 

 maximum accelerations for the surface and pit motion of these three 

 eartliqiiakes are gi\en in the fjlloAving tables. 



(I.) Large undulations. 



