G.H. Darwin: The tides and kindred phenomena in the solar system - Amendments

The word "equal centrifugal forces in magnitude and direction" is thought to have its roots in the book "The tides and kindred phenomena in the solar system" (1898) written by Sir George H. Darwin on tidal phenomena for the general public without using mathematical formulas. Darwin explained translational inertial forces appearing on the earth revolving around a common center of mass by using easy-to-understand "centrifugal force" instead of "inertial force," which is not so familiar to the general public, but this is a misuse of centrifugal force. Darwin probably used "centrifugal force" to mean a force similar to centrifugal force (i.e., inertial force in general) and added the phrase "equal and parallel" to indicate that it is not the usual centrifugal force. This may have misled experts to think that it is acceptable to call this inertial force a centrifugal force. In truth, this force should be called inertial force, not centrifugal force. Here I have tried to correct the mistake in Darwin's book, because if no one points out the mistake, the misunderstanding may not be cleared up forever.

G.H. Darwin:  The tides and kindred phenomena in the solar system (First edition 1898)

p. 96 p. 97 p. 98 p. 99 p. 100

* G.H. Darwin's book can be found at Darwin Online, Project Gutenberg, etc.

Takao Fujiwara, 2022/02