PRESIDENT’S ADDRESS. 53 
we should not know how much of the movement was due 
to the direct action of-those forces, and how much to the 
indirect actions I have indicated. It bas been thought by 
Paschwitz and Ehlert that the records of the horizontal pen- 
dulum at Strassburg show, amidst their other and greater 
perturbations, a periodic oscillation corresponding to the 
direct action of the moon; but it seems unlikely, even if 
such periodic disturbances are well established and deter. 
mined, that we shall ever be able to separate cut the direct 
actions from the indirect, or even able in this way to directly 
measure the tide-producing forces. 
The researches of Dr. S. C. Chandler have shown us pretty. 
conclusively that the axis of rotation of the earth is not co- 
incident with the axis of figure, and that the po’e of the 
rotation axis moves in a small circle in a period of about 427 
days, while at the same time the circle is carried round the 
pole of figure in about one year. Euler had previously 
proved thac, if the earth be regarded as perfectly rigid, the 
period of the oscillation should be but 305 days. If the 
earth is capable, however, of yielding in any way to the 
forces set up when the position of the axis of rotaticn is 
slightly changed. the shape of the earth will undergo cer- 
responding slight alterations. . Newcomb has shown that 
the elasticity of the solid portion of the earth and the 
mobility of the ocean will each have the effect of prolonging 
the period, and S. 8S. Hough has demonstrated that. if the 
period is 427 days, the effective rigidity of the entire earth 
must be glightly greacer than that of steel. One curious, 
result of these investigations is that, if this is correct, there 
shoule be an alteration in the form of the ecean correspond- 
ing co the changes in the position of the axis, which should 
be evident as a minute tide, having a period of 427 days. 
Researches into the tides on the coast of Holland, on the 
Pacific Coast of the United States, and on the Coast of 
Maine, have apparently indicated the real existence of this 
tide. the three results being in fair concord with one another. 
and with Chandler’s results. Examination of other tides is 
in progress. The determination of the earth’s rigidity tuus 
obtained by Hough is about the same as that deduced from 
the values of the fortnightly tide. The results so obtained, 
however, have not been very consistent. 
Tt was pointed out by Newton that if the moon were 
orginally fluid the tidal action of the earth upon it weuld 
cause it to bulge towards the earth, so that the diameter of 
the moon directed towards the earth should be greater than 
the equatorial diameter at right angles to it by an amount 
