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time to time entered into it. Quite recently our Coast and Geodetic Survey has completed the measurement of a line of triangles extending from the Atlantic to the Pacific Oceans. North and south measurements both on the Atlantic and Pacific coasts have been executed or are in progress. The English have from time to time made measures of the same sort in Africa, and the Russians and Germans on their respective territories. Nearly all these measures are now being combined in a work carried on by the International Geodetic Association, of which the geodetic authorities of the principal countries are members.

The latest conclusions on the subject may be summed up thus. We remark in the first place that by the figure of the earth geodetists do not mean the figure of the continents, but of the ocean level as it would be if canals admitting the water of the oceans were dug through the continents. The earth thus defined is approximately an ellipsoid, of which the smaller diameter is that through the poles, and which has about the following dimensions:

Polar diameter, 7,899.6 miles, or 12,713.0 kilometres.

Polar diameter,Equatorial" 7,926.6 miles, or 12,756.5 kilometres.

It will be seen that the equatorial diameter is twenty-seven miles or forty-three kilometres greater than the polar.

What we know of the earth by direct observation is confined almost entirely to its surface. The greatest depth to which man has ever been able to penetrate com-