Tidal Phenomena at Inland Boreholes near Gradock. 93 
to be plausibly divisible into two harmonic components having periods 
of 12 hrs. 26 min. and 12 hrs. respectively. 
These results may be compared with the following principal harmonic 
components of marine tides (see " The Tides," by G. Darwin, p. 182). 
I. Principal lunar semi-diurnal tide : Period, 12 hrs. 25 min . 14^ sec. 
II. Principal solar semi-diurnal tide : Period, 12 hours exactly. 
III. Three diurnal tides : Periods, 23 hrs. 56 min. ; 24 hrs. 4 min. ; 
25 hrs. 49 min. 9f sec. 
The lunar periodicity of the well at least may be regarded as established. 
Tidal Movements of Wells No. III. and No. VI. 
In January, 1912, I spent a week on the farm and devoted my 
attention mainly to preliminary observations on Nos. III. and VI. I 
ascertained that Nos. II., III., and VI. had been continuously open for 
many months. 
I closed Nos. III. and VI. by means of wooden plugs, through which 
projected tightly fitting lead tubes. These lead tubes projected vertically 
about 7 or 8 feet above the plugs, and were surmounted by lengths of glass 
tubing in which one could observe the rise of the water-columns to their 
potential levels. Arbitrary scales were attached to the glass tubes by 
means of which numerical values could be assigned to the levels of the 
water-columns in the tubes. 
During the first few days the levels rose as the wells recovered the loss 
of potential due to their having been open so long. Then readings were 
taken during January 20 and 21. 
The results plotted on squared paper indicate that the mean level 
continued to rise during these days, and that the process of recovery of 
lost potential was still continuously in progress. The theoretical " cone 
of depression " was still filling up around the well. 
The curves, however, show in addition a distinct semi-diurnal fluctuation 
similar to that of No. V. in previous records. On January 21, between 
6 and 7 p.m., No. VI. was opened for 14 minutes, and the effect of this 
is obvious on the No. III. record. This proves a close underground 
communication between No. III. and No. VI. 
I determined the time interval for transmission of change of pressure 
between these two wells as 50 seconds. 
Over No. II. there has been erected a windmill and pump, by means 
of which the water is raised and piped for domestic use into a tank on the 
roof of Mr. Eoberts's house. 
On January 22, about 6 p.m., this mill was put into action, vigorous 
