LE ROY C. COOLEY. Ill 



from time to time and tabulated their values. On com- 

 paring these numerical values he discovered that any 

 two volumes under pressures greater than that of the 

 atmosphere were inversely proportional to the corres- 

 ponding pressures. 



It then remained for him to determine whether the 

 same relation would exist if the pressure should be di- 

 minished more and more below the normal pressure of 

 the atmosphere instead of being raised above it. 



Boyle, accordingly, proceeded as follows : Taking a 

 tube closed at one end he enclosed a portion of air with- 

 in, by nearly filling it with mercury, inverting it in a 

 deep cistern of the same liquid and depressing it until 

 the level was the same in both. At this moment the 

 pressure was that of the atmosphere. On lifting the tube 

 the mercury in it arose also, but more slowly, and the 

 pressure was lessened by an amount always equal to 

 the weight of the column of mercury. As this column 

 lengthened the air above was subjected to pressures less 

 and less. Again the numerical values of the volumes of 

 air and of the corresponding pressures were tabulated, 

 and again it was discovered that the volumes were 

 mathematically proportional inversely to the pressures. 



The statement of Boyle's results generalized has come 

 •down to us in the form of the well-known "Boyle's 

 law," which says that when all other things remain con- 

 stant, the volume of a given mass of air varies inversely 

 as the pressure which it sustains. 



To-day we find this among the most fundamental prin- 

 ciples in the physics of gases, but in 1661 it was the 

 most advanced conception which the human mind had 

 reached. Remember how scanty was the knowledge 

 of nature at that time. The age had scarcely banished 

 the Aristotelian philosophy which attributed all the phe- 

 nomena of atmospheric pressure to " nature's abhorrence 

 of a vacuum." Indeed twenty -five years had not yet 



63 



