EARTHQUAKE MEASUREMENTS IX PIT AND OX SURFACE. 285 



vi1)ratioiis tlic difference is coiLsi(leral)Je. Xow, tlioiigli only ap- 

 proximate tlie calcultition for the ripples may l)e, their maximum 

 velocities and mtixinuim acceljrati<jns are found to he very _UTe:)t, and, 

 in fact, many times greater than those for the principal undulations. 

 And thus', if these ripples are really in great part smoothed away 

 in the ])it, it is \cvy likely that in times of such severe earthquakes as 

 discussed aho\'e, there might ])e less destructive action in deep pits 

 than on the free surface. 



We shall n(jt venture here to discuss what these ripples may be. 

 They exist only in the early part of the sIkjcIvs and seem to be the 

 continuation of the tremors which occur at the beginninii' of earth- 

 quakes. The aj>})earance of the diagrams of the severe earth(|uakes 

 is very much like that of the disturljances in the sea where minute 

 ripples are siiperp<r>ed ou large undulations. If the ripples l3e regard- 

 ed as waves travelling on the surface, then the whole thing will admit 

 of an easy explanation, 



AVe must state ho\ve\er that these observations were made at 

 li(jngo, where the gr()und is hard, and it is needless to say that tlie 

 character of the earthquake motion depends in a great measure on the 

 nature of the soil. Hence it is ([uite possible that observations in 

 different places may lead to scnnewhat different i-esults than those 

 oljfained here. Thus, for instance, at I liiotsul)ashi, where the soil is 

 soft, the range of miction is two or three iimes greater than that at 

 llong(j, and yet the e;!rth(juake diagrams oljtaiiiecl ihere seem to be 

 conq)aratively free of superposed wavelets. 



In the above the observations were confined ro the horizontal 

 conqxjnent motion alone. The usual argument lljr tlie supposed 

 sniallness of the motion at a suljterranean ])oint is derived from the 

 behaviour oi' a row oî ivory balls in ctjntact with each otlier when one 

 at the end is sharply struck. This argument appears to apply rather 



