[page] 546

The Figure of the Earth (not Archdeacon Pratt's).

To the Editor of THE READER

Sir, —Dr. Pratt maintains two propositions, which are incompatible with each other:—

1. That a plumb-line everywhere points to the centre of the earth.

2. That the earth, at the sea level, is not a sphere.

If both are true, it follows that there are places where the plumb-line is not at right angles to the ocean surface, so that the water must there stand permanently out of level. In other words, the forces that determine the direction of the plumb-line, and those that determine the level of fluids, are not the same at the same points on the earth's surface. Will he explain this little difficulty in the way of his peculiar view?

ALFRED R. WALLACE

May 30, 1866.