294 



Art. XI. A Tramlatiori of Rey's Essays on the Cal- 

 cination of Metals, &c. 



[CommuDicated by John GEoncE Children, Esq., F. R. S., Sfc] 

 Continued from page 64. 



Essay XV. 



Air diminishes in weight in three ways. The balance is deceitful, 

 the means of remedying that. 



I RESUME the thread of my discourse, which I had somewhat 

 interrupted to solve the objection advanced against me, and by 

 so much the better clear up this matter ; and I say, that in 

 three preceding essays ; viz., the lOth, 11th, and 12th, I have 

 shewn the three different ways by which air increasing in 

 weight, may manifest that increase when balanced in a free and 

 pure air. Now the law of contraries requires, that, by three ways, 

 the reverse of the former, it may diminish in weight. These 

 ways are the separation of any heavier foreign matter — its exten- 

 sion to more ample bounds, and the abstraction of its heavier 

 parts. But since the knowledge of the former throws sufficient 

 light upon the latter, I omit any fuller explanation ; only 

 begging the reader to observe, that this increase or diminution 

 of weight, of which I have spoken in the said essays, always 

 refers to a portion of air compared with another of equal bulk. 

 For when we do not take the volume of a substance into ac- 

 count, if we examine its weight by reason, I say that nothing 

 gains weight but by the addition of matter, nor loses it but by 

 its subtraction — so inseparably are matter and weight united, 

 as has been shewn above in the sixth essay. But if Ave inves- 

 tigate the subject by the balance, a case occurs in which, with- 

 out any addition or subtraction of matter, a substance will ap- 

 pear more or less heavy ; namely, by its contraction or expan- 

 sion. Now this was the only mode of investigation known to 

 the ancients when they contended that the elements, in their 

 mutual conversion into one another, increase or diminish in 

 weight in proportion as they increase or diminish in'dimension. 



