PEPLY TO PROr. VINCE. "^^^ 



tioned the terms actually employed " as sufficient" for his 

 purpose. 



In the third place, he does not appear to be aware of the Lawofgravita- 

 distinction between physical and mathematical accuracy. Jhem'aitical"^** 

 physically speaking, the series " may certainly'" vary as truth. 



~, with as little sensible errour as the law of gravitation : 



mathematically speaking, we have not the slightest evidence, 



that the law of gravitation " varies accurately'''' as — , and 



in this sense the Professor's assertion is totally void of fouo- 

 /dation. 



The change of the law of density of the medium at the Law of density 

 surface of a planet, instead of being " inconsistent with chaneed with- 

 Newton's hypothesis," is the simple and unavoidable corpse- in a planet. 

 quence of it. Each particle of matter being supposed to 

 induce a certain state of the medium around it indepeiv 

 dently of all others, so that the attraction maybe produced 

 alike in all circumstances, the state of the medium within 

 the planet must necessarily be such, as to product the joint 

 effect of all the attractions; that is, the force must vary as 

 xxy and the density as xx or a a ; the square of the distance 

 from the centre; and this must be the immediate conse- 

 quence of the same cause, that produces the usual variation 

 of density with respect to a single particle- It may be said, 

 that the operation of this cause is equally obscure with the 

 ultimate eifect of gravitation considered as independent of 

 it; and 1 am perfectly ready to admit the objection. I am 

 not defending the Newtonian hypothesis; I am only en- 

 deavouring to show, that Professor Vince has attacked it 

 unsuccessfully, and has heaped errour upon errour in at* 

 tempting to support his arguments. 



I am, Sir, 



Your yery obedient servant, 



9th July, 1808. DYTISCUS. 



VI. 



