MO PRESSURE: IN THE AIR, 



to overcome the resistance of the sides of the 

 vessel in which it is contained.* 



If we proceed to ascertain the relative 

 weights of equal volumes of atmospheric air, 

 when they subsist in the form of rain, or in a 

 dry state ; it will be found that the weight, and 

 inelasticity of the one, will far exceed the levity 

 and expansibility of the other. 



It is to the error of measuring air by 

 weight, instead of expansibility ; and of sub- 

 jecting tb the same laws bodies whose na- 

 ture and properties were totally different 

 from each other, that a great proportion 

 of the false philosophy of the present day 

 is to be ascribed ; it was in subservience 

 to this false philosophy, of measuring air 

 by weight, that Mr. BOYLE himself, so deserv- 

 edly esteemed for eviery quality that was great 

 and good, in order to account for the rise and 



* Pressure and resistance are words which are often con- 

 founded together, but which, nevertheless, have opposite 

 meanings. Pressure is an active force Resistance a passive 

 quality. Thus, when I press my hand against the door, my 

 hand is active, the door passive. A horse which draws a cart, 

 is active, the cart passive. The difference in the nature of 

 each, may, perhaps, be better explained, by comparing re- 

 sistance with pressure, than pressure with resistance. The 

 door cannot press and squeeze my hand, although it can 

 resist the pressure ; it cannot act upon it, although it may be 

 acted upon by it. The cart cannot act upon the horse, al- 

 though it may resist the horse ; the one may, in fact, be 

 considered an active, the other a negative quality. 



