DESCRIPTIO GLOBI INTELLECTUALIS. 283 



of the subject has led me to dwell on it at too much 

 length. 



It is curious to observe that in the interval between 

 the composition of the following tracts and that of the 

 /> Alii/mentis Bacon's leaning against the Copernican 

 in became more decided, though in the same inter- 

 val the system had received an accession of strength, 

 of which doubtless he was not aware, in the discovery 

 of Kepler's third law. 1 This law, connecting as it does 

 the planets with the sun by an uniform relation which 

 i- fulfilled also by the earth, is in some respects the 

 movt remarkable of the three, and points the most di- 

 rectly to the sun as the great centre of our system. No 

 'doubt neither this law, nor all three together, amounts 

 to a positive demonstration : it has sometimes been for- 

 gotten that after all they are but approximations to the 

 truth ; but of all approximations these laws are the 

 most remarkable, and it would be very difficult to doubt, 

 even without the knowledge we now possess, that they 

 are grounded on a physical basis. This basis is their 

 correspondence with a causal or physical approximation. 

 They would be absolutely true if the lesser bodies of 



1 This discorery was made, as Kepler has informed us, on the 15th of 

 1618. In Professor Rigaud's account of Harriot's papers, published 

 >{. it is mentioned that Harriot, who was apparently the first person 

 to determine the periods of Jupiter's satellites, committed an error of cal- 

 culation, in rnii-equence df which that of the first satellite is given at about 

 1 length, but that Harriot, even before the publication in 1614 of 

 .Ini-iiilif, vet-ins to have suspected his error. The Profes- 

 sor eiujuir.^ why he did not try his result by means of Kepler's third law, 

 as we know that he wa< a student of the work in which this law is stated; 

 hat only the first two laws were given in the De Stella Martis, 

 and that in the interval referred to, between 1610 and 1614, Harriot could 

 1,0 iimr.- have known nf Kepler's third law than of Newton's Principia. 

 But it is really curious that Kepler does not seem to have applied his law 

 to the satellites The application is said to have been first made by Ven- 

 dclinus. See Xarrien, Hist, o/" Astronomy, p. 398. 



