Tidal Phenomena at hiland Boreholes near Cradock. 
69 
easily intelligible when it is remembered that the water entered tank A 
through a vertical 6-inch diameter pipe and left by a 5f-inch pipe, nearly 
horizontal, with a fall of only 3 inches in 15 feet. 
As the level of the water surface was found to vary gradually, it 
occurred to me that a series of measurements of the height of this water 
surface would give an indication of the varying pressure at which the 
Fig. 2. 
water issued from the top of the borehole into the tank, and so perhaps 
might afford a more delicate means of determining the variations in the 
yield. An arbitrary datum level was selected 18 inches beneath a certain 
point on the upper rim of the tank, and this datum level served as the 
zero of the following series of vertical measurements: — 
On Jan. 28 at 8 a.m. the level of the water in tank A was 0-25 in. above datum. 
9 a.m. „ „ 0-81 
10.45 a.m. „ „ 1-62 
12.30 p.m. „ „ 2-12 
2.15 p.m. „ „ 2-00 
3.30 p.m. „ „ 1-75 
5.0 p.m. „ „ 1-50 
6.0 p.m. „ „ 1-25 
6.30 p.m. „ „ 1-31 
