8KCT. iv.] DISSERTATION SECOND. 121 



philosophy was of a nature to require time in order to 

 make an impression. It implied an application of mathe- 

 matical reasoning which was often difficult ; the doctrine 

 of prime and ultimate ratios was new to most readers, and 

 could be familiar only to those who had studied the infi- 

 nitesimal analysis. 



The principle of gravitation itself was considered as dif- 

 ficult to be admitted. When presented indeed as a mere 

 fact, like the weight of bodies at the earth's surface, or 

 their tendency to fall to the ground, it was free from ob- 

 jection ; and it was in this light only that Newton wished 

 it to be considered. 1 But though this appears to be the 

 sound and philosophical view of the subject, there has al- 

 ways appeared a strong desire in those who speculated 

 concerning gravitation, to go farther, and to inquire into 

 the cause of what, as a mere fact, they were sufficiently 

 disposed to admit. If you said that you had no explana- 

 tion to give, and was only desirous of having the fact ad- 

 mitted ; they alleged, that this was an unsatisfactory pro- 

 ceeding, — that it was admitting the doctrine of occult cau- 

 ses, — that it amounted to the assertion, that bodies acted in 

 places where they were not, — a proposition that, metaphy- 

 sically considered, was undoubtedly absurd. The desire 

 to explain gravitation is indeed so natural, that Newton 

 himself felt its force, and has thrown out, at the end of 

 his Optics, some curious conjectures concerning this general 

 affection of body, and the nature of that elastic ether to 



1 " Vocem atlractionis hie gcneraliler usurpo pro corporum 

 conatu quvennque acccdcndi ad invicem ; sive conatus iste jiat ab 

 actione corporum se mutuo pctentium, vel per spiritus emisscs se 

 mutvo agitantium; sive is ab actione cetheris, out aeris medii 

 cujiiscunque. corporci vel incorporei, oritur, corpora innatantia in 

 si invicem utcunque impellentes" Principia Math. Lib. I. SchoL 

 ctd finem. prop. G9. 



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