on Mr. HerapatlCi Theory. 295 



"integrity" oi- " honourable feelings." C. distinctly charges 

 me with having intentionally perverted the meaning of the above 

 writers, with having made a disingenuous use of their words, 

 quoted passages in support of Mr. Herapath's theory which have 

 no relation to the subject, &c. The following Prop, which I 

 ■ have given, p. 3G0, Annals for May, and the quotation which 

 I have introduced in the Cor. p. 361, for the expressed pur- 

 pose of showing that the Prop, is compatible with the notion 

 introduced into the old theory of collision, will prove the truth 

 of these charges, and of course C.'s claims to credit and confi- 

 dence. 



Prop. B. Emerson's Tracts, p. 13. 



*' If two perfectly hard, " If a body striking another 



equal, and quiescent balls be gives it any motion, tivice tliat 

 similarly struck by any two body striking the sawe with the 

 other perfectly hard balls, the same velocity will give it ixmcc 

 intensities of the impulses will the motion, and so the motion 

 have a ratio equal to that of generated in the other will be 

 the generating momenta^ as \}i\.<& force of percussion." 



" Except in the absolute equaliti) of reciprocal attraction in 

 the planets," I observed in my first reply, " which Newton de- 

 duced merely from analogy, and of which no proof whatever 

 can be furnished, there is no one pJuenomenon in which Mr. 

 Herapath does not perfectly agree with Newton." C. says, 

 this " assertion possesses as little truth as modesty." This I 

 will certainly allow if C.'s assertions are to be the standard of 

 truth, and his conduct the criterion of modesty ; but not if other 

 people's are. For instance : in reciprocal attraction between 

 different planets, who has proved, and how, that a certain quan- 

 tity of" matter of one planet attracts with the same force that an 

 equal quantity of matter of the other planet does ? Certamly no 

 one; nor can it from any data yet known be done. Newton, 

 Laplace, Lagrange, &c. have analogically suj)posed it to be so; 

 but have never jiroved it. This I will venture to assert C. will 

 not get anj' scientific man of respectable character to contra- 

 dict. So ilir is it from being proved that the different planets 

 attract in j)roportion to their respective quantities of matter, 

 that some j)retty plain facts can be advanced to show the con- 

 trary. Euler, for example, has experimentally demonstrated 

 tliat glass acts upon light to reiract it more powerfully at a high 

 temperature than at a low ; and Newton has Ibimd that " all 

 botlies seem to have their refractive powers proportional to their 

 densities, or very nearly," the temperature being the same; that 

 is, j)r<)portional to their ordinary attractions. Assuming there- 

 lore that the relation between refractive and attractive powers 



holds 



