10 Examination of the Theory of a Resisting Medium. 
existing between them. It is not enough that each particle attracts 
that in contact with it; it must attract the particles that are distant, 
and the intervention of particles between them does not render this 
at all more intelligible.’ (36) We may close this point of investi- 
gation, by arraying Newton against himself. Notwithstanding the 
force with which Newton supposed bodies to be urged by the une- 
qual density of the ether, in certain directions, yet, when treating 
of the tails of comets, his language is, ‘from whence, again, we 
have another argument proving the celestial spaces to be free and 
without resistance, since in them not only the solid bodies of the 
planets and comets, but also the extremely rare vapours of comets’ 
tails maintain their rapid motions with great freedom, and for an ex- 
ceeding long time,”(37) To such and kindred anomalies have the 
greatest minds been occasionally subject, in all ages. 
We have seen that, in 1762, this theory of resistance had so far 
commanded attention that the French Academy offered, in that year, 
a prize for the best examination of it; and we have also seen upon 
what evidences this prize was awarded. The results of the most 
careful modern observation, compared with those of a very ancient 
date, including some eclipses observed at Babylon, as early as 719, 
720, and 721 years before the Christian era, show very clearly that 
the period of the moon’s revolution is shorter in modern than in 
those remote ages.(38) This acceleration, Dr. Halley, the English 
astronomer, in 1695, believed to exist, and declared his conviction 
that he could demonstrate the fact.(39) A more detailed and ex- 
tensive labour of comparison was subsequently performed by the Rev. 
Richard Dunthorne, who, in 1749, published its results, and veri- 
fied the truth of the suspicions of his predecessor.(40) It was the 
cause of this acceleration which the French Academy demanded, 
in 1762. M. Pabbé Bossut sought that cause in the resistance of 
ether ; and believing he had discovered it there, he made such re- 
turns of his labours to the Academy, that the proffered prize was 
awarded him: nor was the errour into which he had fallen, discov- 
(36) Playfair on ms and Phys. Science, pt. 2, Sec. 4. See, also, preface 0 
Newton, by Roger Cot 
(37) Math. Prin. of Nat. Phil. (vide note 12,) vol. 2, p. 369. 
_ (38) Delambre, )’Astronomie au Dix-Huitiéme Siécle, p. 597, note de l’editeur- 
(39) Philosophical Transactions of the Royal Society of London, abridgment 
by Hatton, Shaw and Pearson, vol. 4, p.65. All references to the transactions 
of this Society, made in the course of this article, will be to the same edition here 
designated. 
(40) Ibid. vol. 9, p. 669, a onward. 
