MEMOIR OF KANT.

He therefore sought and obtained employment as a private tutor in distinguished families. He was engaged in this work for nine years and, according to his own candid confession in later years, there was hardly ever a tutor with a better theory or a worse practice. However that may be, he certainly gained the affection of his pupils and the respect of their parents. At the beginning of this period, he published his first work—an essay on the estimation of living force original: vis viva; a 17th- and 18th-century term for what we now call kinetic energy. Toward the end of this period, he published his second—a brief discussion of the question of whether the length of the day has undergone any change. This question had been proposed by the Berlin Academy as the subject for a prize essay. Kant argues that the tides must have the effect of slowing the earth’s rotation, and he provides a rough calculation of the amount of this slowing. His first step toward a predicted approximation was an estimate of the effect of the water’s impulse on the entire east coast of the American continent. His suggestion was sound and wise; however, he vastly overrated the scale of the effect. He inferred that the day had lengthened by about 1.5 seconds in two thousand years. According to Delaunay Charles-Eugène Delaunay (1816–1872), a French astronomer famous for his work on lunar motion, the actual amount of slowing is 1 second in 200,000 years. This result is based on historical facts (the record of eclipses). Kant’s was a purely physical calculation, and for this he did not—

See an essay by the author of this memoir on the Theory of the Tides in the Philosophical Magazine, January 1870, February 1871, and January 1872; and in the Quarterly Journal of Mathematics, March 1872; and on the amount of slowing, Hermathena, 1882. (These essays have now been published in a single volume.) Kant subsequently thought of another cause which might operate in the opposite direction—namely, the condensation of the interior parts of the earth—but he did not publish the suggestion.