308 Transactions of the Boyal Society of South Africa. 
One very remarkable fact is that in the years under discussion there 
was a strong tendency for the pendulum to deviate more and more to the 
v^^est of its mean position during the winter, and to the east during the 
summer. This may be provisionally explained — pending further investi- 
gation — as a tilting of the v/hole sub-continent in response to the loading 
of the east coast by rain in summer and the west coast in winter, supple- 
mented, of course, by the unloading of the west coast in summer by 
evaporation and of the east coast in winter. Be the cause of this what it 
may, the effect is too great to be measured satisfactorily by any means 
at my command.'" 
It is interesting to compare the harmonic elements of temperature and 
barometric pressure (Table 2) with those of the variation of level. In 
each case the time is counted from local mean midnight. In the case of 
the latter element the results are expressed in terms of the deviation in 
millimetres to the west. The near agreement in point of time of the 
second harmonic terms of barometric pressure, temperature variability, 
and variation of level is certainly remarkable. If this is to be regarded as 
having a physical explanation it would seem to be that the original 
gradients set up by the principal agencies — whatever they may be, 
whether temperature or the movement of underground moisture — in the 
ground are modified by the semi-diurnal wave of pressure so that the 
final gradients are actually steeper at the places where the local time 
is 9|- h. a.m. and p.m. 
Perhaps a word in conclusion may not be out of place as to the 
advantages of such a place as Kimberley for seismological research. 
Griqualand West is exactly the uniform and equally exposed prairie-like 
plain that Professor Milne asks for. Moreover, it is almost exactly in the 
centre of the South African Tableland. The great majority of stations in 
the world are not well balanced, so to speak, in their position with refer- 
ence to land and water ; and as a consequence most of them are relatively 
too near the sea to get the diurnal oscillation of level clear of such 
disturbances as are set up by the tides and waves of the ocean. f 
* Observations of the variation of level made at the Eoyal Observatory, Cape Town, 
at a depth of 30 feet, show a tilt to the east in winter, and to the west in summer — just 
the opposite to what is found at Kimberley. The line of greatest winter rain is, as it 
happens, somewhat to the east of Cape Town. This result would seem to confirm the 
suggestion that the annual oscillation of level is due to incidence of rainfall. 
t For an interesting discussion of the general question see a paper by Prof. E. 
Lagrange, on " Periodicite Sismique," in Bulletin de la Societe beige d' Astronomie, 
July, 1904. It appears from this that the diurnal variation of level at Uccle is 
extremely feeble. At Strassburg, four times as far from the sea, it is much greater. 
Mr. T. F. Claxton, in Remits of Mag. and Met. Observations made at Mauritius in 
190(3, mentions the curious fact that when the Milne seismograph of the Port Alfred 
Observatory was removed from the electrometer hut to the magnet basement the phase 
was changed by approximately 12 hours and the amplitude reduced to about one-fourth. 
