Atmosphere. 97 



short, the nature and constitution of all 

 matter would be changed and cease; wan- 

 ting this universal bond and constituting 

 principle* 



As to the weight and pressure of the 

 air, it is evident that the mass of the at- 

 mosphere, in common with all other mat- 

 ter, must be endued with weight and 

 pressure ; and this principle was asserted 

 by almost all philosophers, both ancient 

 and modern. But it was only by means 

 of the experiments made with pumps and 

 the barometrical tube, by Galileo and 

 Torricelli, that we came to the proof, not 

 only that the atmosphere is endued with 

 a pressure, but also what the measure 

 and quantity of that pressure is. Thus it 

 is found, that the pressure of the atmos- 

 phere sustains a column of quicksilver, in 

 the tube of the barometer, of about thirty 

 inches in height : it therefore follows, 

 that the whole pressure of the atmosphere 

 is equal to the weight of a column of quick 

 silver, of an equal base, and thirty inches 

 height: and, because a cubical inch of 

 quicksilver is found to weigh nearly half 

 a pound avoirdupois, therefore the whole 

 thirty inches, or the weight of the atmosr 



