322 Sir William Thomson on the Ultramundane 



not ascribe innate gravity to me. That gravity should be innate, 

 inherent, and essential to matter, so that one body may act upon 

 another at a distance through a vacuum, without the mediation 

 of any thing else, by and through which their action and force 

 may be conveyed from one to another, is to me so great an 

 absurdity, that I believe no man who has in philosophical matters 

 a competent faculty of thinking, can ever fall into it. Gravity 

 must be caused by an agent acting constantly according to certain 

 laws; but whether this agent be material or immaterial, I have 

 left to the consideration of my readers." — Newton's Third 

 Letter to Bentley, February 25th, 1692-3. 



" Nobody surely, in his sober senses, has ever pretended to 

 understand the mechanism of gravitation ; and yet what sublime 

 discoveries was our immortal Newton enabled to make, merely 

 by the investigation of the laws of its action " *. 



Le Sage expounds his theory of gravitation, so far as he had 

 advanced it up to the year 1782, in a paper published in the 

 Transactions of the Royal Berlin Academy for that year, under 

 the title " Lucrece Newtonien." His opening paragraph, en- 

 titled " But de ce memoire," is as follows : — 



" Je me propose de faire voir : que si les premiers Epicuriens 

 avoient eu ; sur la Cosmographie des idees aussi saines seule- 

 ment, que plusieurs de leurs contemporains, qu'ils negligeoient 

 d'ecouter f j et sur la Geometrie, une partie des connoissances qui 

 etoient deja communes alors : ils auroient, tres probablement, 

 decouvert sans effort ; les Loix de la Gravite universelle, et sa 

 Cause mecanique. Loix ; dont l'invention et la demonstration, 

 font la plus grande gloire du plus puissant genie qui ait jamais 

 existe : et Cause, qui apres avoir fait pendant longtems, Pam- 

 bition des plus grands Physiciens ; fait a present, le desespoir de 

 leurs sucesseurs. De sorte que, par exemple, les fameuses Regies 

 de Kepler; trouvees il y a moins de deux siecles, en partie sur 

 des conjectures gratuites, et en partie apres d'immenses taton- 

 nemens ; n' auroient ete que des corollaires particuliers et inevi- 

 tables, des lumieres gen erales que ces ancien s Philosophes pouvoient 

 puiser (comme en se jouant) dans le mecanisme proprement dit 

 de la Nature. Conclusion ; qu'on peut appliquer exactement 

 aussi, aux Loix de Galilee sur la chute des Graves sublunaires ; 

 dont la decouverte a ete plus tardive encore, et plus contestee : 

 joint a ce que, les experiences sur lesquelles cette decouverte etoit 

 etablie; laissoient dans leurs resultats (necessairement grossiers), 



* "An Inquiry concerning the Source of the Heat which is excited by 

 Friction. By Count Rumford," Philosophical Transactions, 1/98. 



f " Vobis (Epicureis) minus notum est, quemadmodum quidque dicatur. 

 Vestra enim solum legitis, vestra amatis ; cseteros, causa, incognita, con- 

 demnatis. — Ciceron, De naiura Decrum, ii. 29." 



