refpeSfitg Heat or Caloric, ' J ^5 



confidered as convertible. When a diminution of the fpecific 

 gravity is declared, an increafe of the abfolute gravity is by 

 the fame enunciation afTerted, whether the fpeaker means lo 

 do fo or not. Now, in the cafe before dated, the diniinu-' 

 tion of the fpecific gravity is admitted ; and therefore a qnef- 

 tion naturally prefents itfelf^ — Why has the increafe of abfo- 

 lute weiorht not been hitherto obferved ? I take the reafon to 

 be this : they attempted to determine it in the air; overlook- 

 ing this plain faft, namely, that air may be confidered as 

 bearing the fame relation to heat that water does to gold, or 

 rather, to a fubftance many times heavier, if fuch could be 

 found ; that is, the air, though a rarer fubftance than the 

 folid bodies weighed in it, isadenfer one than heat; and 

 they have been demanding, that a fubftance fpecifically 

 lighter than air ftiould defcend in it. In other words : that 

 the laws of nature fhould be inverted, and that the heavier 

 fluid, air, ihould afcend to make room for a lighter one^ heat, 

 to defcend. 



But Nature will not bend to our whims and fancies. We 

 mnft court her, and take her as ftie is, or remain in error. 

 The heated body, though increafed in fize, remains in equi- 

 librium in the balance; and it ought to do fo (if not to 

 afcend), being buoyed up by a greater quantity of air than 

 before it was heated. But is this the only cafe in which 

 that effecl: takes place, and where we know at the fame time 

 that not only volume but real fubftance is added to one end 

 of the beam ? No : a bladder capable of eafily containing a 

 gallon of air will always weigh the fame (in air) whether 

 you put into it a pint, a quart, or a gallon. 



Aye, fays a cavillcR, but you have not put into the bladder 

 cny thing heavier than the furrounding medium, though you 

 have put in a real gravitating fubftance ; therefore the bladder 

 cannot weigh heavier. Inftead of anfwering him, I fliall leave 

 him to his own meditations. 



Are philofophers always to continue in the belief that 

 bodies can be made fpecifically lighter and heavier at plea- 

 fure, without any thing being either abftra6ted or added > 

 Can a nonentity produce the effefts of which we have been 

 fpeakipg ? or, is gravity itfelf a nonentity ? It either is, or 



heat 



