SHISMIG BERFECTS Wal 
cular to the original direction of g, the potential W» will give 
rise to an accelerating force 
which is operative in deflecting the pendulum. But this is 
not the whole matter. The Earth yields to the disturbing 
potential W. and, in accordance with a well-established prin- 
ciple, the surface is deformed by an earth tide of amount 
AW,/¢ and the deformation of both earth and sea produces an 
extra potential AW2. Thus the additional force operative on 
the pendulum mass becomes 
(1 +2) 
OW, 
on 
instead of 
wW, 
On 
The tide ZW,/g, however, produces a tilt in the platform 
h IW, 
so that the recorded displacement of the pendulum zero will 
appear to be proportional to 
Py) 
(2+) Mm 
2 
or 
instead of 
W, 
Oe 
as it would be if the Earth did not yield. 
In a similar way it appears that the oceanic tide becomes 
(1 -h+£)W3/g in place of Wo/g. 
When the potential W2 is expressed in terms of the lati- 
tude and longitude and the co-ordinates of Sun or Moon, we 
obtain a number of terms representing the component tides. 
Chief among these are the approximately semi-diurnal lunar 
and solar terms, and for reasons that do not appear quite 
adequate, attention has until recently been concentrated on 
the corresponding terms in the pendulum zero movement. 
The experiments begun by Zollner and Rebeur-Paschwitz 
have been repeated by others, and the most recent observations 
