G. F. Becker — Kant as a Natural Philosopher. Ill 



declivities which can be attacked and transported by rain 

 water."* 



In 1754, according to Kant, the Berlin Academy offered a 

 prize for a solution of the question "Whether the rotation of 

 the earth which produces the alternation of day and night, has 

 undergone any change since the time of its origin? TV hat is 

 the cause and how can the fact be established ?" f Kant's 

 paper printed in the same year dealt with both the tidal retarda- 

 tion of the moon Avhile still in a fluid state, and the retardation 

 of the earth's rotation by the marine tides. The subject seems 

 then to have fallen into complete oblivion for nearly seventy 

 years. The retardation of the moon's rotation was rediscovered 

 by Laplace in 1824. The earth's retardation was maintained 

 by Prof. James Thomson in conversation about 1840, as Lord 

 Kelvin mentions.;}; J. R. Mayer expressed the same opinion in 

 print in 1848.§ Helmholtz in 1854 discussed the tidal retarda- 

 tion both of the moon and of the earth. || William Ferrel and 

 C. Delaunay afterwards again suggested tidal retardation of the 

 earth. It was only at a later date that Kant's paper was 

 brought to light. 



So far as I know, J. J. von Littrow, in 1830, was the first to 

 revive the Kantian idea of a final collapse of the solar system. T 

 In 1854 Helmholtz again recurred to it. He explains the 

 future annihilation of the rotation of the planets by tidal 

 friction, and relies on a certain inevitable amount of resistance 

 in interplanetary space to destroy orbital motion. Thomson 

 and Tait, in 1867, showed that after the earth has come to 

 expose to the moon a constant aspect, the effect of the solar 

 tides will be to reduce the distance between earth and moon 

 until they come together. By a similar argument it is said to 

 follow that loss of energy (irrespective of a resisting medium) 

 will not cease until all the bodies of the solar system "subside 

 into a state of motion in circles round an axis passing through 

 their center of inertia, like parts of one rigid body." - * It does 



* Kant's Werke, vol. i, p. 203. 



f I find in the memoirs of the Academy no mention of this prize, and Kant's 

 paper printed in 1754 does not seem to have been offered in the competition. 

 Peschel and Leipoldt, however, refer to it as having taken the prize. (Physische 

 Erdknnde, vol. i, 1884, p. 54.) 



^Geological Time, Address G-eol. Soc. Glasgow, Feb. 27, 1868. 



§ Beitrage zur Dynamik des Himmels, Heilbronn, 1848. Translated in Phil. 

 Mag., vol. xxv, 1863, p. 403. 



| Popularwissenschaftliche Vortrage, 2d Fascicle, p. 130. 



T In Vorlesungen liber Astronomie, second part 1830, p. 146, he announces this 

 approaching catastrophe and ascribes it to external influences acting on the sys- 

 tem. Later he indicated friction in a resisting medium as the external influence. 

 This explanation probably appeared in the first edition of his work. Die Wunder 

 des Himmels, 1834. 



** Nat. Phil., 2d ed., sec. 276. The text of this section is the same as in the 

 first edition of 1867. 



