INTRODUCTION. IS 



distinctly adduces tlie tides as evidence^ that the attract; vfr 

 Ibrce of the moon {virtus tractoria) extends to the earth ; 

 and that this force, similar to that exerted by the magnet 

 on iron, would deprive the earth of its water ii the formes 

 should cease to attract it. Unfortunately, this great mai? 

 was induced, ten years afterward, in 1619, prohahly from 

 deference to Galileo, who ascribed the ebb and flow of the 

 ocean to the rotation of the earth, to renounce his correct 

 explanation, and depict the earth in the Harmonice Munch 

 as a living monster, whose whale-like mode of breathing oc- 

 casioned the rise and fall of the ocean in recurring periods 

 of sleeping and waking, dependent on solar time. "VVlien we 

 remember the mathematical acumen that pervades one of the 

 works of Kepler, and of v/hich Laplace has already made 

 honorable mention,! it is to be lamented that the discoverer 

 of the three great laws of all planetary niotion should not 

 have advanced on the path whither he had been led by his 

 views on the attraction of the masses of cosmical bodies. 



Descartes, who was endowed with greater versatility of 

 physical knowledge than Kepler, and who laid the founda- 

 tion of many departments of mathematical physics, under- 

 took to comprise the whole world of phenomena, the heav- 



* " Si Terra cessaret attraliere ad se aquas suas, aquae manna? oranes 

 elevareiitur et in corpus Luna? influerent. Orbis virtutis tractorise, qure 

 est in Luna, porrigitur usque act terras, et prolectat aquas quacunque 

 pi verticem loci incidit sub Zonam torridam, quippe in occursura suura 

 quacunque in verticem loci incidit, insensibiliter in maribus inclusis, 

 sensibiliter ibi ubi sunt latissimi alvei Oceani propinqui, aquisque spa- 

 ciosa reciprocationis libertas." (Kepler, 1. c.) " Undas a Luna trahi 

 7it ferrum a Magnete." .... Kepleri Harmonice Mundi, libri quinque, 

 1G19, lib. iv., cap. 7 , p. 162. The same work which presents us with 

 so many admirable views, among others, with the data of the establisb 

 inent of the third la^o (that the squares of the periodic times of two 

 planets are as the cubes of their mean distance), is distorted by the 

 wildest flights of fancy on the respiration, nutrition, and heat of tho 

 earth-animal, on the soul, memory {memoria animcB Terrcc), and crea« 

 tive imagination {animce Telluns imaginatio) of this monster. This great 

 rian was so wedded to these chimeras, that he warmly contested his 

 right of priority in the views regarding the earth-animal with the mys- 

 tic author of the Macrocosmos, Robert Fludd, of Oxford, who is report- 

 ed to have participated in the invention of the thermometer. {Harm. 

 Mnndi, p. 252.) In Kepler's writings, the attraction of masses is often 

 confounded with magnetic attraction. " Corpus solis esse magneticum. 

 Virtutem, quae Planetas movet, residere in corpore eolis." — Stella Mar- 

 its, pars iii., cap. 32, 34. To each planet was ascrired a mcgnetic axig^ 

 which constantly pointed to one and tlie same quivvter of the heavens 

 f Apelt, Jok. Kfple/s Astron. IVeltansicht, 1849, s. 73. 



t Compare Cosmos vol. ii., p. 327 (and note 



