62 PROCEEDINGS OF SECTION A. 
ance of the proper conduct of this work in the interests of 
the shipping, the fact that it is the basis of all hydrography 
and of all charts, and the scientific importance of having a 
proper systematic method of work whereby our knowledge 
may be continuaily added to, are all, 1 chink, weighty 
reasons in favour of my suggestion. 
Many attempts have been made to directly measure the 
horizontal component of the tide-producing force. This 
will clearly tend to deflect a pendulum from the vertical in a 
regular periodic way. The amount of this deflection is ex- 
cessively small. On a pendulum 10 feet long the maximum 
effect is about «55 inch. Scill, the measurement of 
this would not present any insuperable difficulty if it were 
not complicated by other disturbances. If the earth were 
perfectly rigid, the cbserved deflection should coincide with 
the calculated; but, if the solid earth itself is deformed by 
the action of the tidal forces, the difference between the 
observed and calculated deflections would enable us to form 
some idea of the amount of the earth’s deformation, and, 
consequently, of the rigidity of the solid earth. The most 
notable of these attempts was made by the Brothers Darwin 
in 1879, but it would seem that all such attempts are doomed 
to failure, principally on account of the instability of the 
earth whereon we stand. The pressure of a light wind on 
the walls of the house, for instance, tilts the ground, and 
alters the apparent direction of the vertical to a much 
greater extent than do the forces we seek to measure. 
Further, we now know that the tidal forces would produce: 
indirect effects upon the direction of the vertical, especially 
near the sea-shore, which would frequently be considerably 
greater than the direct one. Thus, when it is high tide 
along a coast, the water is heaped up all along the shore to a 
depth of several feet greater than mean sea-level. This 
water will have a direct attractive effect upon a pendulum 
hung a little distance inland. Further, the weight of the 
thousands of extra tons of water on the coast must deform. 
the surface ‘of the earth in its vicinity, and consequently 
produce an apparent deflection of the vertical. The actual 
effect upon a pendulum would thus be ja combination of the 
direct attraction of the water with the effect.due to the 
warping of the $oil under the influence of the weight of that 
water. This action of the tide upon the pendulum has 
been observed in several cases, and such effects are clearly 
co-periodic with the tideproducing forces. Thus, even if 
it were possible to determine periodic oscillations of a pen- 
dulum synchronising with the lunar tidegenerating forces, 
