ON THE EARTHQUAKE AND VOLCANIC PHENOMENA OF JAPAN. 91 



imagined that between February 28 and March 3 the dip of the rocks 

 increased and then decreased through an angle of 4"-0S. About the same 

 time the movement at right angles to this was 2"-88. With the exception 

 of a wave indicated by C between February 6 and 7, which had a period of 

 I'i hours, all the other movements have had periods of from 48 to 70 

 hours. In this respect the movements are strikingly different from those 

 recorded in Tokio, where diurnal waves are very frequent. Another 

 remarkable feature in the records is the entire absence of tremors, which 

 in Tokio on the alluvium often result in producing a photographic trace from 

 .5 to 10 millimetres, and sometimes even more than this, in breadth (Plate 

 II., figs. 5 and 6). Although it is premature to offer an explanation for the 

 Kamakura movements the following statement may be made. As the 

 changes in temperature in the cave were usually too small to be measur- 

 able it is not likely that the wandering of the pendulums can be attributed 

 to such a cause. Any effect that the heat of the sun may have had upon 

 the face of the cliff in which the cave is situated, in raising its tempera- 

 ture or by v/ithdrawing moisture from its surface, would probably be 

 diurnal in its character. The only sunshine records which I have taken 

 commence on February 25. From that day to February 28 there were 28 

 hours of sunshine which was followed by dull weather until March 11. 

 Although the end of the period of sunshine was followed by a great move- 

 ment, considerable movements occurred during the comparatively cloudy 

 weather. Because the records are few this observation, however, cai-ries but 

 little weight. Rain, which only fell between February 8 and 9, and again 

 between March 5 and 6, does not show any connection with the movements. 

 Notwithstanding these observations, since the wandering of pendulums in 

 Tokio, as will be shown later, is apparently connected with the movement 

 of subterranean water, which in turn is related to percolation from the 

 surface, it does not seem unlikely that the movements at Kamakura may 

 also find a partial explanation in a somewhat similar cause. The only 

 other explanation, which, however, has not yet been verified, is that they 

 result from rock crumpling which is still in progress, and for this reason 

 the greatest motion is parallel to the dip. 



Conclusions of practical importance which I arrive at are that although 

 pendulums which will record a tilting of 0"-3 are sufficiently sensitive to 

 be used on the Tokio plain, an instrument of much greater sensibility is 

 required to study movements on the rock, and, further, that all who have 

 to carry out physical investigations requiring a steady platform will gain 

 great advantage by installations on the rock where tilting is small and 

 diurnal movements and tremors are not appreciable to instruments such 

 as I have employed. 



(e) Earthquakes. 



The earthquakes which have been recorded by the Kamakura instru- 

 ments in 1893 are as follows : — 



The following 26 disturbances are clearly shown upon the photographic 

 traces. In addition to these there are a number of slight irregularities with 

 amplitudes of 1 mm., or under, which have been omitted, first, because 

 they are very small, and secondly, because they might or might not be due 

 to earth disturbances. While the observations were going on, that is, 

 between January 14 and March 18, by means of seismographs in Tokio, 21 

 shocks were recorded. These were disturbances that were felt in Tokio, and 

 it is known that several of them were also felt in Kamakura. It is probable 



