The smallest diameter of the earth is that measured from pole to pole
along the axis of rotation; this is 7,899.6 miles, or about 500,000,000
inches. The greatest diameters are those measured between opposite
points on the equator; these are 7,926.6 miles, and, therefore, show
that the eccentricity of the earth, or the extent of its departure from
the perfect sphere, is very slight.
The circumference of the earth, measured along the equator, is 24,899
miles; the area is 197,000,000 square miles; and the volume is
260,000,000,000 cubic miles. Experiments on the comparative attraction
of the earth show that its density is about five and one-half times
that of pure water. Its mass is, therefore, approximately six thousand
trillion tons.