Tidal Phenomena at Inland Boreholes near Cradock. 91 
about the afternoon of June 5 or the morning of June 6. Then it slowly 
declines to a minimum about the afternoon of June 7. 
Next it slowly rises, attaining a maximum somewhere in the morning 
of June 9, after which it falls to a minimum in the morning of June 13. 
Following this comes the most noteworthy movement of the curve. 
It rises more rapidly than usual, attaining the highest of all the maxima 
in the afternoon June 14, and remains very high from that point to the 
end in June 17, though a slight downward movement marks the last two 
days of its course. During June 14, 15, and 16 the line is continuously 
higher than in any other part of the fortnight. 
It has been already remarked that the barograph curves taken on the 
farm during this fortnight indicated comparatively little variation of 
atmospheric pressure during the period. 
A close examination shows that the barogram for the fortnight contains 
two principal maxima and three minima. 
A slight downward movement begins in the morning of June 5, and 
a minimum is reached about 4 p.m. on June 6, after which a slight upward 
movement culminates in a maximum about 11 a.m. on June 7. Then a 
slight downward movement follows, reaching a minimum about noon on 
June 9, after which a gradual upward movement carries the curve to a 
maximum at 9 a.m., June 13. 
Now follows the greatest movement of the fortnight. The line falls 
about -2 of an inch between the last-mentioned time and the minimum at 
6 p.m. of June 14. From that date on to the morning of June 18 there is 
little movement. 
A comparison of the curve H with the barograph curve makes it 
apparent that the former is substantially the vertical inversion of the 
latter, the maxima of the one corresponding in time to the minima of 
the other. 
Let us return now to the consideration of the residual curve D. 
Although this curve is obviously more uniformly regular than curve A, 
nevertheless it is apparent that it contains more than one harmonic 
component. This is indicated by the varying amplitudes of its waves. 
The obvious interpretation is that it consists of two harmonics whose 
periods do not differ much from each other — both being approximately 
semi-diurnal periods. In the middle of the fortnight when the amplitudes 
of curve D are smallest a minimum point of one of the harmonics syn- 
chronises with a maximum point of the other harmonic component. At 
the beginning and end of the fortnight when the amplitudes are greatest 
the maxima of the one harmonic tend to coincide with the maxima of the 
other harmonic. Now in the middle of the fortnight the moon was in its 
first quarter. One of the general results already obtained from the very 
