29(5 D.'s Second Reply to C. 



holds good in any one body ; and that when its refractive power 

 is augmented or diminished, its attraction also is augmented or 

 diminished, which is by no means improbable, we should say 

 that as the further planets must be colder than the nearer, the 

 attractions of the former ought to be less than those of the lat- 

 ter. In other words, the apparent densities of the planets, 

 which are the measures of then- attractions, should diminish as 

 we recede from the sun ; — a circumstance which experience 

 proves. 



Again, the mean distances of comets from the sun being 

 much greater than of the planets, we should apprehend their 

 attractions ought to be much less; which is actually the case. 

 Laplace, Playfair, and others, say their actions are totally in- 

 sensible. A comet in 14-54 eclipsed the moon, yet it produced 

 no effects on the moon's or earth's motion. One in liVS came 

 so near the earth as to sweep over 120 degrees in one day ; and 

 another in 1770 passed almost among Jupiter's satellites; yet 

 neither of them deranged in the least sensible degree the mo- 

 tions of the bodies to which it so closely approached. 



A difference has likewise been noticed by Mr, Herapath, 

 Annals for June 1821, p. 411, between the observed and La- 

 place's computed annual equation to the moon's mean motion, 

 which would seem to show that the earth attracts the moon 

 more strongly when nearer the sun than when further ; as, for 

 instance, stronger in December than in June, Magnetic, elec- 

 tric, &c, atti-actions are also well known to be influenced by 

 the temperature. So that on all hands there is the greatest 

 reason to believe that " the absolute equality of reciprocal at- 

 traction in the planets," is not true, however confidently C. 

 may pour out his unsupported assertions to the contraiy, 



I dislike quibbling comment on the meaning of terms ; and 

 therefore I pass over C's observations on Mr. H.'s differing 

 from Newton on an imaginary case of bodies inclosed in a 

 space and supposed devoid of all attractive tendency, which he 

 attempts to palm on the world as aphcvnomeiioii; that is, (as Dr. 

 Hutton observes,) as "an appearance in physics discovered by 

 observation of the celestial bodies or by physical experiments," 

 There are, however, some that would from this circumstance 

 tell C, he has as much to learn of the meaning of scientific 

 terms as of science itself, " before," as he has observed of Mr. 

 H., " he can attain among scientific men that rank to which he 

 seems to aspire," 



C's explanation or apology for his "pushing case" is cu- 

 rious indeed. He quotes what he had written, which is a clear 

 proof of charging Mr. H. " with confounding pressure with 

 impulse;" and then he makes a kind of supplicatory appeal 



iio-ainst 



