von Sterneek and General Defforges. Numerous
observations have been made in all parts of the world by various
explorers, and have led to a fairly complete knowledge of the
distribution of gravity over the surface of the globe. Thus we have
succeeded in making evident anomalies which would not easily find
their place in the formula of Clairaut.
Another constant, the determination of which is of the greatest
utility in astronomy of position, and the value of which enters into
electromagnetic theory, has to-day assumed, with the new ideas on the
constitution of matter, a still more considerable importance. I refer
to the speed of light, which appears to us, as we shall see further
on, the maximum value of speed which can be given to a material body.
After the historical experiments of Fizeau and Foucault, taken up
afresh, as we know, partly by Cornu, and partly by Michelson and
Newcomb, it remained still possible to increase the precision of the
measurements. Professor Michelson has undertaken some new researches
by a method which is a combination of the principle of the toothed
wheel of Fizeau with the revolving mirror of Foucault.
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