90 



REPORT — 1895. 



millimetre in C a tilt of about 2" would be required. Between February 

 IS and 25 the same deflection was obtained by a tilt of about 0"-27. 

 Because D recorded more motion than C, it is important to notice that this 

 occurred notwithstanding the fact that on all occasions, excepting between 

 February 4 and February 11, C was very much more sensitive than D. 



Sensitiveness of C and B. 



The temperature variations in the cave during 24 hours never exceeded 

 l°o C. 



((■) The Diagrams. 



At first sight, with the exception of places where earthquakes have 

 been recorded, the photographic traces appear to be a series of long 

 straight lines, and the fact that movements have taken place to the right 

 and left of a normal position can in most cases only be seen by looking 

 along their length (see fig. 2, Plate II.). The cui-ves which are thus 

 seen are too long and flat to admit of accurate measurement, and although 

 the films had only moved at a rate of about 6 mm. per hour there is great 

 uncertainty in determining points of inflection. For these i-easons both 

 the angular deflections and the periods occupied in describing them are 

 only rough approximations. In the diagrams, Plate III., the observations 

 extending over nine weeks are plotted as a series of curves. The vertical 

 lines indicate noon and midnight of successive days, which are marked with 

 their dates. The horizontal lines, which are 10 mm. apart, indicate seconds 

 of arc. If the curve for C goes downwards from its starting point the 

 movement is equivalent to a rising on the S.E. side, while if the D curve 

 descends this means that the S.W. rises. The angular values for the 

 various deflections are marked on the diagrams, while earthquakes recorded 

 by seismographs but not by the pendulums are indicated by dots. Earth- 

 quakes recorded by the pendulums but not by seismographs are shown by 

 short straight lines. 



(d) The Movements of the Pendulums. 



From the diagrams it is clearly seen that during any week the pendulums 

 have once or twice wandered away from and then returned to their 

 starting point. Because the movements or j^eriods of comparative rest of 

 the two instruments approximately coincide in time, as, for example, during 

 the fifth week, I take it that the cause of these movements is something 

 more genei'al than a warping of the supporting columns. The movement 

 of D or that which is parallel to the dip has usually been greater than 

 that indicated by C or parallel to the strike. For example, it may be 



