Affinity of the Elements of Atmospheric Air, 79 



authorities, and more limited abilities, would permit. I 

 wish to excite no controversy, neither will I enter into any 

 on this subject. But nullitis in verba : I will hold such 

 opinions as I have reason to think well founded. I have 

 shown all the deference which plain dealing would allow, 

 to the deservedly respected author from whom 1 dissent — ■ 

 only because I really do not think he has treated one of the 

 greatest men whom this island or the world ever produced, 

 with alt that candour (for Roger Bacon needs no indul- 

 gence) which is always attached to the name of Dr. S. I 

 have, in short, endeavoured to observe the happy mean 

 which Sir Richard Steele recommends, when he says, that 

 zeal and candour are two very good things, if we can but 

 contrive to keep fire out of the one and frost out of the 

 other. Yours, &c. 



*D. 



XVI. On the supposed Chemical Affinity of the Elements of 

 AtmospJieric Air : with Remarks upon Dr, Thomson's Ob- 

 servations on this Subject, 



To Mr, Tilloch, 



SIR, 



-Ln a former letter inserted in your Magazine (vol. xiv. 

 p. 169.), I endeavoured to show the absurdity of the notion 

 of atmospherical air being a chemical compound of azotic 

 and oxvgenous gases. Besides the difficulty, or rather im- 

 possibility, on the one hand, of conceiving how two ele- 

 mentary particles, constantly repelling each other, should, 

 notwithstanding, be held together by a principle of cohesion 

 or chemical affinity ;— or, on the other hand, supposing the 

 two atoms to combine and form one centre of repulsion, 

 how atmospheric air should differ from nitrous gas, &c. 

 there are a variety of facts which oppose the doctrine so 

 forcibly, that I have for some time wondered on what 

 grounds those who are still its adherents defended it. Dr. 

 Thomson, in the 2d edition of his Chemistry, vol. hi. 

 page 316, after reviewing the opinions of different philoso- 

 phers on this head, and amongst others my own, concludes 

 that air is a chemical compound : he assigns the four fol- 

 lowing reasons for the conclusion, which, from his exten- 

 sive acquaintance with authorities, may fairly, it is pre- 

 sumed, be deemed the most cogent that have been offered 

 on that side of the question. It is the object of this com- 

 munication to show their insufficiency. 



1. The 



