lOi RETORT— 1895. 



on the surface, while in six cases it has been less than that on the surface. 

 These instances are taken from the three or four clay periods. If the 

 analysis was made for daily periods, the difference between the amount 

 of motion recorded underground and that recorded on the surface would 

 be yet more marked. Whenever the movements of the surface instrument 

 A have been great, exceeding 1" in seven instances, its direction of 

 motion has corresponded with the direction of movement of the instru- 

 ment which is placed in a parallel direction F. In two cases the directions, 

 of movement between A and F have been opposite to each other. When, 

 however, the movements of A have been small or less than 1" the cases of 

 agreement and of disagreement in direction of motion are practically 

 equal, there being 6 of one and 11 of the other. For January, February,, 

 and March rainfall seems to have been followed by considerable dis- 

 turbances underground, the movements during dry periods being compara- 

 tively small. The instrument on the surface has, however, shown several 

 marked exceptions to the latter rule, its pointer having moved from 8 to 

 12 mm. (2" to 3") at least five times when the displacement could not be 

 attributed to the saturation of the soil. 



During April and May, although a considerable amount of rain fell, 

 the movements of the underground instruments were small, but it must be 

 remembered that during these months percolation was in all probability 

 very small as compared with that of January, February, and March. 

 Instrument A, on the contrary, showed on several occasions very large 

 movements between April 13 and 14, moving as much as 30 mm. or 6", and 

 from what has gone before it is not necessary to assume that these dis- 

 turbances were directly connected with rainfall. 



Up to the date of writing this report I have not been able to obtain, 

 from the Meteorological DejDartment factors which enable me to make 

 any accurate estimate of the ratio of percolation to evaporation, but it 

 may be taken, as a general rule, that percolation and the fluctuations in 

 height of subterranean water are greater during the winter montlis than 

 they are during the summer, and if the instruments partly owe their move- 

 ments to movements of underground water, these movements ought to be 

 most pronounced in winter, and this seems to have been the case. Since the 

 commencement of May, up to June 6, E and F have wandered but little, the 

 diagrams being fine straight lines like fig. 1, Plate II., and without tremors. 

 It must also be observed that it has been the instruments in the under- 

 ground chambers within 1 2 feet of water level which have moved the most.. 



To throw additional light upon the part that subterranean water may 

 have played in influencing the motion of the pendulums the following 

 experiments were made : — 



1. The movements of water in an unused well were recorded. 



2. A rough measurement of the rate at which moisture was evaporated! 

 from ground near to one of the instruments was made. 



3. A well near to one of the instruments was twice emptied of its 

 water. 



(k) Moveiiients of Water in a Well. 



From April 18 until June 8, I established a tide gauge in an unused 

 ■well 80 yai'ds to the east of the underground chamber. It consisted of 

 a large M'ooden float carrying a bamboo mast 30 feet in length, the top of 

 which projected through a hole in a lid which covered the top of the well. 

 As the mast rose and fell a pencil in contact with a sheet of paper on a drum 



